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[PATCH v15 6/8] Row pattern recognition patch (docs). 165+ messages / 2 participants [nested] [flat]
* [PATCH v15 6/8] Row pattern recognition patch (docs). @ 2024-03-28 10:30 Tatsuo Ishii <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Tatsuo Ishii @ 2024-03-28 10:30 UTC (permalink / raw) --- doc/src/sgml/advanced.sgml | 80 ++++++++++++++++++++++++++++++++++++ doc/src/sgml/func.sgml | 54 ++++++++++++++++++++++++ doc/src/sgml/ref/select.sgml | 38 ++++++++++++++++- 3 files changed, 170 insertions(+), 2 deletions(-) diff --git a/doc/src/sgml/advanced.sgml b/doc/src/sgml/advanced.sgml index 755c9f1485..cf18dd887e 100644 --- a/doc/src/sgml/advanced.sgml +++ b/doc/src/sgml/advanced.sgml @@ -537,6 +537,86 @@ WHERE pos < 3; <literal>rank</literal> less than 3. </para> + <para> + Row pattern common syntax can be used to perform row pattern recognition + in a query. Row pattern common syntax includes two sub + clauses: <literal>DEFINE</literal> + and <literal>PATTERN</literal>. <literal>DEFINE</literal> defines + definition variables along with an expression. The expression must be a + logical expression, which means it must + return <literal>TRUE</literal>, <literal>FALSE</literal> + or <literal>NULL</literal>. The expression may comprise column references + and functions. Window functions, aggregate functions and subqueries are + not allowed. An example of <literal>DEFINE</literal> is as follows. + +<programlisting> +DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +</programlisting> + + Note that <function>PREV</function> returns the price column in the + previous row if it's called in a context of row pattern recognition. So in + the second line the definition variable "UP" is <literal>TRUE</literal> + when the price column in the current row is greater than the price column + in the previous row. Likewise, "DOWN" is <literal>TRUE</literal> when when + the price column in the current row is lower than the price column in the + previous row. + </para> + <para> + Once <literal>DEFINE</literal> exists, <literal>PATTERN</literal> can be + used. <literal>PATTERN</literal> defines a sequence of rows that satisfies + certain conditions. For example following <literal>PATTERN</literal> + defines that a row starts with the condition "LOWPRICE", then one or more + rows satisfy "UP" and finally one or more rows satisfy "DOWN". Note that + "+" means one or more matches. Also you can use "*", which means zero or + more matches. If a sequence of rows which satisfies the PATTERN is found, + in the starting row of the sequence of rows all window functions and + aggregates are shown in the target list. Note that aggregations only look + into the matched rows, rather than whole frame. In the second or + subsequent rows all window functions and aggregates are NULL. For rows + that do not match the PATTERN, all window functions and aggregates are + shown AS NULL too, except count which shows 0. This is because the + unmatched rows are in an empty frame. Example of + a <literal>SELECT</literal> using the <literal>DEFINE</literal> + and <literal>PATTERN</literal> clause is as follows. + +<programlisting> +SELECT company, tdate, price, + first_value(price) OVER w, + max(price) OVER w, + count(price) OVER w +FROM stock, + WINDOW w AS ( + PARTITION BY company + ORDER BY tdate + ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING + AFTER MATCH SKIP PAST LAST ROW + INITIAL + PATTERN (LOWPRICE UP+ DOWN+) + DEFINE + LOWPRICE AS price <= 100, + UP AS price > PREV(price), + DOWN AS price < PREV(price) +); +</programlisting> +<screen> + company | tdate | price | first_value | max | count +----------+------------+-------+-------------+-----+------- + company1 | 2023-07-01 | 100 | 100 | 200 | 4 + company1 | 2023-07-02 | 200 | | | + company1 | 2023-07-03 | 150 | | | + company1 | 2023-07-04 | 140 | | | + company1 | 2023-07-05 | 150 | | | 0 + company1 | 2023-07-06 | 90 | 90 | 130 | 4 + company1 | 2023-07-07 | 110 | | | + company1 | 2023-07-08 | 130 | | | + company1 | 2023-07-09 | 120 | | | + company1 | 2023-07-10 | 130 | | | 0 +</screen> + </para> + <para> When a query involves multiple window functions, it is possible to write out each one with a separate <literal>OVER</literal> clause, but this is diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml index 93b0bc2bc6..d25eeb3327 100644 --- a/doc/src/sgml/func.sgml +++ b/doc/src/sgml/func.sgml @@ -22637,6 +22637,7 @@ SELECT count(*) FROM sometable; returns <literal>NULL</literal> if there is no such row. </para></entry> </row> + </tbody> </tgroup> </table> @@ -22676,6 +22677,59 @@ SELECT count(*) FROM sometable; Other frame specifications can be used to obtain other effects. </para> + <para> + Row pattern recognition navigation functions are listed in + <xref linkend="functions-rpr-navigation-table"/>. These functions + can be used to describe DEFINE clause of Row pattern recognition. + </para> + + <table id="functions-rpr-navigation-table"> + <title>Row Pattern Navigation Functions</title> + <tgroup cols="1"> + <thead> + <row> + <entry role="func_table_entry"><para role="func_signature"> + Function + </para> + <para> + Description + </para></entry> + </row> + </thead> + + <tbody> + <row> + <entry role="func_table_entry"><para role="func_signature"> + <indexterm> + <primary>prev</primary> + </indexterm> + <function>prev</function> ( <parameter>value</parameter> <type>anyelement</type> ) + <returnvalue>anyelement</returnvalue> + </para> + <para> + Returns the column value at the previous row; + returns NULL if there is no previous row in the window frame. + </para></entry> + </row> + + <row> + <entry role="func_table_entry"><para role="func_signature"> + <indexterm> + <primary>next</primary> + </indexterm> + <function>next</function> ( <parameter>value</parameter> <type>anyelement</type> ) + <returnvalue>anyelement</returnvalue> + </para> + <para> + Returns the column value at the next row; + returns NULL if there is no next row in the window frame. + </para></entry> + </row> + + </tbody> + </tgroup> + </table> + <note> <para> The SQL standard defines a <literal>RESPECT NULLS</literal> or diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml index 066aed44e6..8f18718d58 100644 --- a/doc/src/sgml/ref/select.sgml +++ b/doc/src/sgml/ref/select.sgml @@ -969,8 +969,8 @@ WINDOW <replaceable class="parameter">window_name</replaceable> AS ( <replaceabl The <replaceable class="parameter">frame_clause</replaceable> can be one of <synopsis> -{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ] -{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ] +{ RANGE | ROWS | GROUPS } <replaceable>frame_start</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax] +{ RANGE | ROWS | GROUPS } BETWEEN <replaceable>frame_start</replaceable> AND <replaceable>frame_end</replaceable> [ <replaceable>frame_exclusion</replaceable> ] [row_pattern_common_syntax] </synopsis> where <replaceable>frame_start</replaceable> @@ -1077,6 +1077,40 @@ EXCLUDE NO OTHERS a given peer group will be in the frame or excluded from it. </para> + <para> + The + optional <replaceable class="parameter">row_pattern_common_syntax</replaceable> + defines the <firstterm>row pattern recognition condition</firstterm> for + this + window. <replaceable class="parameter">row_pattern_common_syntax</replaceable> + includes following subclauses. <literal>AFTER MATCH SKIP PAST LAST + ROW</literal> or <literal>AFTER MATCH SKIP TO NEXT ROW</literal> controls + how to proceed to next row position after a match + found. With <literal>AFTER MATCH SKIP PAST LAST ROW</literal> (the + default) next row position is next to the last row of previous match. On + the other hand, with <literal>AFTER MATCH SKIP TO NEXT ROW</literal> next + row position is always next to the last row of previous + match. <literal>DEFINE</literal> defines definition variables along with a + boolean expression. <literal>PATTERN</literal> defines a sequence of rows + that satisfies certain conditions using variables defined + in <literal>DEFINE</literal> clause. If the variable is not defined in + the <literal>DEFINE</literal> clause, it is implicitly assumed + following is defined in the <literal>DEFINE</literal> clause. + +<synopsis> +<literal>variable_name</literal> AS TRUE +</synopsis> + + Note that the maximu number of variables defined + in <literal>DEFINE</literal> clause is 26. + +<synopsis> +[ AFTER MATCH SKIP PAST LAST ROW | AFTER MATCH SKIP TO NEXT ROW ] +PATTERN <replaceable class="parameter">pattern_variable_name</replaceable>[+] [, ...] +DEFINE <replaceable class="parameter">definition_varible_name</replaceable> AS <replaceable class="parameter">expression</replaceable> [, ...] +</synopsis> + </para> + <para> The purpose of a <literal>WINDOW</literal> clause is to specify the behavior of <firstterm>window functions</firstterm> appearing in the query's -- 2.25.1 ----Next_Part(Thu_Mar_28_19_59_25_2024_076)-- Content-Type: Text/X-Patch; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="v15-0007-Row-pattern-recognition-patch-tests.patch" ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
* [PATCH] Teach REPACK to upgrade its lock safely. @ 2026-04-14 09:59 Antonin Houska <[email protected]> 0 siblings, 0 replies; 165+ messages in thread From: Antonin Houska @ 2026-04-14 09:59 UTC (permalink / raw) REPACK (CONCURRENTLY) needs to upgrade its ShareUpdateExclusiveLock (SUEL) to AccessExclusiveLock at the end of table processing. If another session, which already has a non-conflicting lock on the table, tried to get SUEL too, it would end up in a deadlock with REPACK. Such situation does not hurt as long as the deadlock detector choses to terminate the other session, but it's possible that it terminates REPACK. A lot of REPACK's work would be wasted this way. This patch checks for such situation, and if the other session tries to get the SUEL, it receives a deadlock report before it actually starts waiting. Please note that the other session can safely run VACUUM w/o receiving the deadlock report. The point is that VACUUM cannot run in a transaction block, so the session cannot have any other lock when trying to get SUEL on the table. In that case, REPACK gets its AccessExclusiveLock first, even if VACUUM requested SUEL earlier. VACUUM then just needs wait for REPACK to finish, and then it can start. --- src/backend/commands/repack.c | 25 +++++++- src/backend/storage/lmgr/deadlock.c | 10 ++-- src/backend/storage/lmgr/lock.c | 30 ++++++++++ src/backend/storage/lmgr/proc.c | 55 ++++++++++++++++- src/include/storage/lock.h | 5 +- src/include/storage/proc.h | 6 +- .../injection_points/expected/repack.out | 59 ++++++++++++++++++- .../injection_points/specs/repack.spec | 29 +++++++++ 8 files changed, 209 insertions(+), 10 deletions(-) diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c index 58e3867246f..e9193067666 100644 --- a/src/backend/commands/repack.c +++ b/src/backend/commands/repack.c @@ -285,6 +285,18 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel) * to understand and we don't lose any functionality. */ PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)"); + + /* + * Also set the PROC_IN_CONCURRENT_REPACK flag. This makes the lock + * manager cause anyone that would conflict with us to error out. + * It's important to set this flag ahead of actually locking the + * relation; it won't of course affect anyone until we do have a lock + * that others can conflict with. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); } /* @@ -3086,7 +3098,18 @@ rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHeap, LockRelationOid(OldHeap->rd_rel->reltoastrelid, AccessExclusiveLock); /* - * Tuples and pages of the old heap will be gone, but the heap will stay. + * Now that we have all access-exclusive locks on all relations, we no + * longer want other processes to error out when trying to acquire a + * conflicting lock. Therefore, unset our flag. + */ + LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE); + MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK; + ProcGlobal->statusFlags[MyProc->pgxactoff] = MyProc->statusFlags; + LWLockRelease(ProcArrayLock); + + /* + * Tuples and pages of the old heap will be gone, but the heap itself will + * stay. */ TransferPredicateLocksToHeapRelation(OldHeap); foreach_ptr(RelationData, index, indexrels) diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c index b8962d875b6..3772a7aa3df 100644 --- a/src/backend/storage/lmgr/deadlock.c +++ b/src/backend/storage/lmgr/deadlock.c @@ -1146,8 +1146,10 @@ DeadLockReport(void) void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, - LOCK *lock, - PGPROC *proc2) + LOCK *lock, /* XXX Only lockmode? */ + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2) { DEADLOCK_INFO *info = &deadlockDetails[0]; @@ -1155,8 +1157,8 @@ RememberSimpleDeadLock(PGPROC *proc1, info->lockmode = lockmode; info->pid = proc1->pid; info++; - info->locktag = proc2->waitLock->tag; - info->lockmode = proc2->waitLockMode; + info->locktag = *locktag2; + info->lockmode = lockmode2; info->pid = proc2->pid; nDeadlockDetails = 2; } diff --git a/src/backend/storage/lmgr/lock.c b/src/backend/storage/lmgr/lock.c index c221fe96889..44aa2ca26a7 100644 --- a/src/backend/storage/lmgr/lock.c +++ b/src/backend/storage/lmgr/lock.c @@ -674,6 +674,36 @@ LockHeldByMe(const LOCKTAG *locktag, return false; } +/* + * HaveRelLock -- test whether the current backend has a fast path lock on + * the relation in any mode. + */ +bool +HaveFastPathLock(Oid relid) +{ + uint32 group = FAST_PATH_REL_GROUP(relid); + bool result = false; + + LWLockAcquire(&MyProc->fpInfoLock, LW_SHARED); + for (int i = 0; i < FP_LOCK_SLOTS_PER_GROUP; i++) + { + uint32 f = FAST_PATH_SLOT(group, i); + uint32 lockmask; + + if (relid != MyProc->fpRelId[f]) + continue; + lockmask = FAST_PATH_GET_BITS(MyProc, f); + if (lockmask) + { + result = true; + break; + } + } + LWLockRelease(&MyProc->fpInfoLock); + + return result; +} + #ifdef USE_ASSERT_CHECKING /* * GetLockMethodLocalHash -- return the hash of local locks, for modules that diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 1ac25068d62..3d47b1284a3 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1156,6 +1156,7 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) LOCKMASK myHeldLocks; bool early_deadlock = false; PGPROC *leader = MyProc->lockGroupLeader; + bool check_repack = false; Assert(LWLockHeldByMeInMode(partitionLock, LW_EXCLUSIVE)); @@ -1193,6 +1194,56 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) } } + /* + * If I am already holding this lock (in any mode) and trying to get + * ShareUpdateExclusiveLock (or higher), check if REPACK (CONCURRENTLY) is + * already holding ShareUpdateExclusiveLock. The problem is if that by + * trying to upgrade the lock to AccessExclusiveLock it would get into a + * deadlock with us. + */ + if (lock->tag.locktag_type == LOCKTAG_RELATION && + lock->tag.locktag_field1 == MyDatabaseId && + lockmode >= ShareUpdateExclusiveLock) + { + if (myHeldLocks > 0 || + HaveFastPathLock(lock->tag.locktag_field2)) + check_repack = true; + } + if (check_repack) + { + dlist_iter iter; + + dlist_foreach(iter, &lock->procLocks) + { + PROCLOCK *otherproclock; + PGPROC *otherproc; + + otherproclock = dlist_container(PROCLOCK, lockLink, iter.cur); + otherproc = otherproclock->tag.myProc; + if (otherproc != MyProc && + otherproc->statusFlags & PROC_IN_CONCURRENT_REPACK) + { + LOCKMASK repackmask = otherproclock->holdMask; + + /* + * Is REPACK already holding ShareUpdateExclusiveLock? + */ + if ((repackmask & LOCKBIT_ON(ShareUpdateExclusiveLock)) != 0) + { + /* + * There should be no more than one REPACK working on + * particular table, so let's error out. + */ + RememberSimpleDeadLock(MyProc, lockmode, lock, + otherproc, + ShareUpdateExclusiveLock, + &otherproclock->tag.myLock->tag); + return PROC_WAIT_STATUS_ERROR; + } + } + } + } + /* * Determine where to add myself in the wait queue. * @@ -1240,7 +1291,9 @@ JoinWaitQueue(LOCALLOCK *locallock, LockMethod lockMethodTable, bool dontWait) * a flag to check below, and break out of loop. Also, * record deadlock info for later message. */ - RememberSimpleDeadLock(MyProc, lockmode, lock, proc); + RememberSimpleDeadLock(MyProc, lockmode, lock, proc, + proc->waitLockMode, + &proc->waitLock->tag); early_deadlock = true; break; } diff --git a/src/include/storage/lock.h b/src/include/storage/lock.h index ee3cb1dc203..85804d61ce9 100644 --- a/src/include/storage/lock.h +++ b/src/include/storage/lock.h @@ -401,6 +401,7 @@ extern void LockReleaseCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern void LockReassignCurrentOwner(LOCALLOCK **locallocks, int nlocks); extern bool LockHeldByMe(const LOCKTAG *locktag, LOCKMODE lockmode, bool orstronger); +extern bool HaveFastPathLock(Oid relid); #ifdef USE_ASSERT_CHECKING extern HTAB *GetLockMethodLocalHash(void); #endif @@ -440,7 +441,9 @@ pg_noreturn extern void DeadLockReport(void); extern void RememberSimpleDeadLock(PGPROC *proc1, LOCKMODE lockmode, LOCK *lock, - PGPROC *proc2); + PGPROC *proc2, + LOCKMODE lockmode2, + LOCKTAG *locktag2); extern void InitDeadLockChecking(void); extern int LockWaiterCount(const LOCKTAG *locktag); diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 3e1d1fad5f9..76c6bb44251 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -70,10 +70,12 @@ struct XidCache #define PROC_AFFECTS_ALL_HORIZONS 0x20 /* this proc's xmin must be * included in vacuum horizons * in all databases */ +#define PROC_IN_CONCURRENT_REPACK 0x40 /* REPACK (CONCURRENTLY) */ -/* flags reset at EOXact */ +/* flags reset at EOXact. A bit of a misnomer ... */ #define PROC_VACUUM_STATE_MASK \ - (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND) + (PROC_IN_VACUUM | PROC_IN_SAFE_IC | PROC_VACUUM_FOR_WRAPAROUND | \ + PROC_IN_CONCURRENT_REPACK) /* * Xmin-related flags. Make sure any flags that affect how the process' Xmin diff --git a/src/test/modules/injection_points/expected/repack.out b/src/test/modules/injection_points/expected/repack.out index b575e9052ee..960044776f4 100644 --- a/src/test/modules/injection_points/expected/repack.out +++ b/src/test/modules/injection_points/expected/repack.out @@ -1,4 +1,4 @@ -Parsed test spec with 2 sessions +Parsed test spec with 3 sessions starting permutation: wait_before_lock change_existing change_new change_subxact1 change_subxact2 check2 wakeup_before_lock check1 injection_points_attach @@ -111,3 +111,60 @@ injection_points_detach (1 row) + +starting permutation: check1_relnode_only wait_before_lock lock3 wakeup_before_lock check1_relnode_only +injection_points_attach +----------------------- + +(1 row) + +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 1 +(1 row) + +step wait_before_lock: + REPACK (CONCURRENTLY) repack_test USING INDEX repack_test_pkey; + <waiting ...> +step lock3: + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; + +i|j +-+- +1|1 +(1 row) + +ERROR: deadlock detected +step wakeup_before_lock: + SELECT injection_points_wakeup('repack-concurrently-before-lock'); + +injection_points_wakeup +----------------------- + +(1 row) + +step wait_before_lock: <... completed> +step check1_relnode_only: + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; + +count +----- + 2 +(1 row) + +injection_points_detach +----------------------- + +(1 row) + diff --git a/src/test/modules/injection_points/specs/repack.spec b/src/test/modules/injection_points/specs/repack.spec index d727a9b056b..5ffcb558718 100644 --- a/src/test/modules/injection_points/specs/repack.spec +++ b/src/test/modules/injection_points/specs/repack.spec @@ -55,6 +55,13 @@ step check1 FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j) WHERE d1.i ISNULL OR d2.i ISNULL; } +step check1_relnode_only +{ + INSERT INTO relfilenodes(node) + SELECT relfilenode FROM pg_class WHERE relname='repack_test'; + + SELECT count(DISTINCT node) FROM relfilenodes; +} teardown { SELECT injection_points_detach('repack-concurrently-before-lock'); @@ -129,6 +136,20 @@ step wakeup_before_lock SELECT injection_points_wakeup('repack-concurrently-before-lock'); } +session s3 +# Try to acquire SharedUpdateExclusiveLock on a table while REPACK is already +# holding it and before it tries to upgrade it to AccessExclusiveLock. Since +# this session is already holding another lock no the table, REPACK cannot +# resolve the problem by getting ahead in the wait queue. The solution is that +# the LOCK TABLE triggers a deadlock report. The deadlock does not actually +# take place, but it would if this session started to wait. +step lock3 +{ + BEGIN; + SELECT * FROM repack_test ORDER BY i LIMIT 1; + LOCK TABLE repack_test IN SHARE UPDATE EXCLUSIVE MODE; +} + # Test if data changes introduced while one session is performing REPACK # CONCURRENTLY find their way into the table. permutation @@ -140,3 +161,11 @@ permutation check2 wakeup_before_lock check1 + +# See 'lock3' above. We check relnodes to make sure that REPACK finished. +permutation + check1_relnode_only + wait_before_lock + lock3 + wakeup_before_lock + check1_relnode_only -- 2.47.3 --=-=-=-- ^ permalink raw reply [nested|flat] 165+ messages in thread
end of thread, other threads:[~2026-04-14 09:59 UTC | newest] Thread overview: 165+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2024-03-28 10:30 [PATCH v15 6/8] Row pattern recognition patch (docs). Tatsuo Ishii <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]> 2026-04-14 09:59 [PATCH] Teach REPACK to upgrade its lock safely. Antonin Houska <[email protected]>
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