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[PATCH v45 7/8] Error out any process that would block at REPACK
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* [PATCH v45 7/8] Error out any process that would block at REPACK
@ 2026-03-25 19:35 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-03-25 19:35 UTC (permalink / raw)

Any process waiting on REPACK to release its lock would actually cause
it to deadlock when it tries to upgrade its lock to AEL, losing all work
done to that point.  We avoid this by teaching the deadlock detector to
raise an error when this condition is detected.
---
 src/backend/commands/repack.c                 | 53 ++++++++----
 src/backend/storage/lmgr/deadlock.c           | 15 ++++
 src/include/storage/proc.h                    |  6 +-
 src/test/modules/injection_points/Makefile    |  1 +
 .../expected/repack_deadlock.out              | 63 ++++++++++++++
 src/test/modules/injection_points/meson.build |  1 +
 .../specs/repack_deadlock.spec                | 83 +++++++++++++++++++
 7 files changed, 202 insertions(+), 20 deletions(-)
 create mode 100644 src/test/modules/injection_points/expected/repack_deadlock.out
 create mode 100644 src/test/modules/injection_points/specs/repack_deadlock.spec

diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d25ab43da7b..7291b4180ab 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -276,6 +276,16 @@ ExecRepack(ParseState *pstate, RepackStmt *stmt, bool isTopLevel)
 	/* Determine the lock mode to use. */
 	lockmode = RepackLockLevel((params.options & CLUOPT_CONCURRENT) != 0);
 
+	/*
+	 * If in concurrent mode, set the PROC_IN_CONCURRENT_REPACK flag.  This
+	 * makes the deadlock checker 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.
+	 */
+	if ((params.options & CLUOPT_CONCURRENT) != 0)
+		MyProc->statusFlags |= PROC_IN_CONCURRENT_REPACK;
+
 	/*
 	 * If a single relation is specified, process it and we're done ... unless
 	 * the relation is a partitioned table, in which case we fall through.
@@ -476,11 +486,8 @@ RepackLockLevel(bool concurrent)
  * If indexOid is InvalidOid, the table will be rewritten in physical order
  * instead of index order.
  *
- * Note that, in the concurrent case, the function releases the lock at some
- * point, in order to get AccessExclusiveLock for the final steps (i.e. to
- * swap the relation files). To make things simpler, the caller should expect
- * OldHeap to be closed on return, regardless CLUOPT_CONCURRENT. (The
- * AccessExclusiveLock is kept till the end of the transaction.)
+ * On return, OldHeap is closed but locked with AccessExclusiveLock - the lock
+ * will be released at end of the transaction.
  *
  * 'cmd' indicates which command is being executed, to be used for error
  * messages.
@@ -512,10 +519,12 @@ cluster_rel(RepackCommand cmd, Relation OldHeap, Oid indexOid,
 		/*
 		 * Make sure we're not in a transaction block.
 		 *
-		 * The reason is that repack_setup_logical_decoding() could deadlock
-		 * if there's an XID already assigned.  It would be possible to run in
-		 * a transaction block if we had no XID, but this restriction is
-		 * simpler for users to understand and we don't lose anything.
+		 * The reason is that repack_setup_logical_decoding() could wait
+		 * indefinitely for our XID to complete. (The deadlock detector would
+		 * not recognize it because we'd be waiting for ourselves, i.e. no
+		 * real lock conflict.) It would be possible to run in a transaction
+		 * block if we had no XID, but this restriction is simpler for users
+		 * to understand and we don't lose anything.
 		 */
 		PreventInTransactionBlock(isTopLevel, "REPACK (CONCURRENTLY)");
 
@@ -998,10 +1007,8 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
 		 * Note that the worker has to wait for all transactions with XID
 		 * already assigned to finish. If some of those transactions is
 		 * waiting for a lock conflicting with ShareUpdateExclusiveLock on our
-		 * table (e.g.  it runs CREATE INDEX), we can end up in a deadlock.
-		 * Not sure this risk is worth unlocking/locking the table (and its
-		 * clustering index) and checking again if it's still eligible for
-		 * REPACK CONCURRENTLY.
+		 * table (e.g. it runs CREATE INDEX), it should encounter ERROR in the
+		 * deadlock checking code.
 		 */
 		start_repack_decoding_worker(tableOid);
 
@@ -3119,10 +3126,18 @@ 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.
+	 */
+	MyProc->statusFlags &= ~PROC_IN_CONCURRENT_REPACK;
+
+	/*
+	 * Tuples and pages of the old heap will be gone, but the heap itself will
+	 * stay.  In order for predicate locks to continue to work, convert them
+	 * to relation-level locks.  We do this both for table and indexes.
 	 */
 	TransferPredicateLocksToHeapRelation(OldHeap);
-	/* The same for indexes. */
 	for (int i = 0; i < nind; i++)
 	{
 		Relation	index = ind_refs[i];
@@ -3342,9 +3357,11 @@ start_repack_decoding_worker(Oid relid)
 
 	/*
 	 * The decoding setup must be done before the caller can have XID assigned
-	 * for any reason, otherwise the worker might end up in a deadlock,
-	 * waiting for the caller's transaction to end. Therefore wait here until
-	 * the worker indicates that it has the logical decoding initialized.
+	 * for any reason, otherwise the worker might end up waiting for the
+	 * caller's transaction to end. (Deadlock detector does not consider this
+	 * a conflict because the worker is in the same locking group as the
+	 * backend that launched it.) Therefore wait here until the worker
+	 * indicates that it has the logical decoding initialized.
 	 */
 	ConditionVariablePrepareToSleep(&shared->cv);
 	for (;;)
diff --git a/src/backend/storage/lmgr/deadlock.c b/src/backend/storage/lmgr/deadlock.c
index b8962d875b6..3d3ec0da111 100644
--- a/src/backend/storage/lmgr/deadlock.c
+++ b/src/backend/storage/lmgr/deadlock.c
@@ -620,6 +620,21 @@ FindLockCycleRecurseMember(PGPROC *checkProc,
 						proc->statusFlags & PROC_IS_AUTOVACUUM)
 						blocking_autovacuum_proc = proc;
 
+					/*
+					 * Similarly, if we note that we're blocked by some process
+					 * running REPACK (CONCURRENTLY), just fail.  That process
+					 * is going to upgrade its lock at some point, and it would
+					 * be inappropriate for any other process to cause that
+					 * to fail.
+					 */
+					if (checkProc == MyProc &&
+						proc->statusFlags & PROC_IN_CONCURRENT_REPACK)
+						ereport(ERROR,
+								errcode(ERRCODE_OBJECT_IN_USE),
+								errmsg("could not wait for concurrent REPACK"),
+								errdetail("Process %d waits for REPACK running on process %d",
+									   MyProc->pid, proc->pid));
+
 					/* We're done looking at this proclock */
 					break;
 				}
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1dad125706e..8ad9718f3d6 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -69,10 +69,12 @@ 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/Makefile b/src/test/modules/injection_points/Makefile
index 2cd7d87c533..f7663859fe2 100644
--- a/src/test/modules/injection_points/Makefile
+++ b/src/test/modules/injection_points/Makefile
@@ -15,6 +15,7 @@ REGRESS_OPTS = --dlpath=$(top_builddir)/src/test/regress
 ISOLATION = basic \
 	    inplace \
 	    repack \
+	    repack_deadlock \
 	    repack_toast \
 	    syscache-update-pruned \
 	    heap_lock_update
diff --git a/src/test/modules/injection_points/expected/repack_deadlock.out b/src/test/modules/injection_points/expected/repack_deadlock.out
new file mode 100644
index 00000000000..a86e4767536
--- /dev/null
+++ b/src/test/modules/injection_points/expected/repack_deadlock.out
@@ -0,0 +1,63 @@
+Parsed test spec with 2 sessions
+
+starting permutation: wait_before_lock add_column wakeup_before_lock check1
+injection_points_attach
+-----------------------
+                       
+(1 row)
+
+step wait_before_lock: 
+	REPACK (CONCURRENTLY) repack_deadlock USING INDEX repack_deadlock_pkey;
+ <waiting ...>
+step add_column: 
+	alter table repack_deadlock add column noise text;
+ <waiting ...>
+step add_column: <... completed>
+ERROR:  could not wait for concurrent REPACK
+step wakeup_before_lock: 
+	SELECT injection_points_wakeup('repack-concurrently-before-lock');
+
+injection_points_wakeup
+-----------------------
+                       
+(1 row)
+
+step wait_before_lock: <... completed>
+step check1: 
+	INSERT INTO relfilenodes(node)
+	SELECT relfilenode FROM pg_class WHERE relname='repack_deadlock';
+
+	SELECT count(DISTINCT node) FROM relfilenodes;
+
+	SELECT i, j FROM repack_deadlock ORDER BY i, j;
+
+	INSERT INTO data_s1(i, j)
+	SELECT i, j FROM repack_deadlock;
+
+	SELECT count(*)
+	FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j)
+	WHERE d1.i ISNULL OR d2.i ISNULL;
+
+count
+-----
+    1
+(1 row)
+
+i|j
+-+-
+1|1
+2|2
+3|3
+4|4
+(4 rows)
+
+count
+-----
+    4
+(1 row)
+
+injection_points_detach
+-----------------------
+                       
+(1 row)
+
diff --git a/src/test/modules/injection_points/meson.build b/src/test/modules/injection_points/meson.build
index a414abb924b..1cd88d6db65 100644
--- a/src/test/modules/injection_points/meson.build
+++ b/src/test/modules/injection_points/meson.build
@@ -46,6 +46,7 @@ tests += {
       'basic',
       'inplace',
       'repack',
+      'repack_deadlock',
       'repack_toast',
       'syscache-update-pruned',
       'heap_lock_update',
diff --git a/src/test/modules/injection_points/specs/repack_deadlock.spec b/src/test/modules/injection_points/specs/repack_deadlock.spec
new file mode 100644
index 00000000000..9d23a6588c2
--- /dev/null
+++ b/src/test/modules/injection_points/specs/repack_deadlock.spec
@@ -0,0 +1,83 @@
+# Test REPACK with a concurrent transaction that would cause a deadlock
+setup
+{
+	CREATE EXTENSION injection_points;
+
+	CREATE TABLE repack_deadlock(i int PRIMARY KEY, j int);
+	INSERT INTO repack_deadlock(i, j) VALUES (1, 1), (2, 2), (3, 3), (4, 4);
+
+	CREATE TABLE relfilenodes(node oid);
+
+	CREATE TABLE data_s1(i int, j int);
+	CREATE TABLE data_s2(i int, j int);
+}
+
+teardown
+{
+	DROP TABLE repack_deadlock;
+	DROP EXTENSION injection_points;
+
+	DROP TABLE relfilenodes;
+	DROP TABLE data_s1;
+	DROP TABLE data_s2;
+}
+
+session s1
+setup
+{
+	SELECT injection_points_set_local();
+	SELECT injection_points_attach('repack-concurrently-before-lock', 'wait');
+}
+# Perform the initial load and wait for s2 to do some data changes.
+step wait_before_lock
+{
+	REPACK (CONCURRENTLY) repack_deadlock USING INDEX repack_deadlock_pkey;
+}
+# Check the table from the perspective of s1.
+#
+# Besides the contents, we also check that relfilenode has changed.
+
+# Have each session write the contents into a table and use FULL JOIN to check
+# if the outputs are identical.
+step check1
+{
+	INSERT INTO relfilenodes(node)
+	SELECT relfilenode FROM pg_class WHERE relname='repack_deadlock';
+
+	SELECT count(DISTINCT node) FROM relfilenodes;
+
+	SELECT i, j FROM repack_deadlock ORDER BY i, j;
+
+	INSERT INTO data_s1(i, j)
+	SELECT i, j FROM repack_deadlock;
+
+	SELECT count(*)
+	FROM data_s1 d1 FULL JOIN data_s2 d2 USING (i, j)
+	WHERE d1.i ISNULL OR d2.i ISNULL;
+}
+teardown
+{
+	SELECT injection_points_detach('repack-concurrently-before-lock');
+}
+
+session s2
+# Change the existing data. UPDATE changes both key and non-key columns. Also
+# update one row twice to test whether tuple version generated by this session
+# can be found.
+step add_column
+{
+	alter table repack_deadlock add column noise text;
+}
+
+step wakeup_before_lock
+{
+	SELECT injection_points_wakeup('repack-concurrently-before-lock');
+}
+
+# Test if data changes introduced while one session is performing REPACK
+# CONCURRENTLY find their way into the table.
+permutation
+	wait_before_lock
+	add_column
+	wakeup_before_lock
+	check1
-- 
2.47.3


--cldir6umqisr673d
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v45-0008-Teach-snapshot-builder-to-skip-transactions-runn.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v52 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--gp2pyozrd5pweboh
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v52-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v53 7/7] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 92759f33969..6ba86384312 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qr3jlalmmcpkiodg--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v54 5/5] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 86 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 ++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 117 insertions(+), 63 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index d3fea738ca3..a90d163e416 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d1be6c60e88..ec3a2cd441d 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3382,7 +3382,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index c85166ba849..39cbb0252f4 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -223,7 +223,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -232,8 +232,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -244,6 +244,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index dc46a372ead..06efcaa60b2 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -308,6 +308,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -328,6 +329,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -344,7 +346,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 9533515a63b..47679161b67 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -151,6 +151,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -188,14 +190,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -208,7 +211,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -222,7 +225,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -372,6 +375,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -379,10 +383,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -431,12 +436,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -444,7 +453,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -454,7 +465,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -547,7 +559,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -575,7 +587,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -869,7 +882,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1251,7 +1264,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1306,7 +1319,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1373,12 +1386,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1453,11 +1466,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1514,13 +1527,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1617,11 +1630,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1655,17 +1668,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2216,7 +2236,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2224,7 +2244,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2329,7 +2349,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2430,7 +2450,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..9d7d675fa96 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1240,7 +1240,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1309,6 +1309,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1466,7 +1467,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a315c4ab8ab..bf82b8f6048 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2071,6 +2071,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 6d0337853e0..fb75990609e 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..489af7d8d6c 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -377,7 +378,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--cdhh4t7ukb6tnjoq--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v50 8/8] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 78 ++++++++++++-------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  6 +-
 12 files changed, 96 insertions(+), 46 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index fdb77df0fdb..a87626a01b6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d6e446d582d..2fc30008f59 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3383,7 +3383,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..1bc7f3f600d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..49fb10df038 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,9 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
+int			TotalMaxReplicationSlots = 0;	/* sum of both */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -191,12 +194,14 @@ ReplicationSlotsShmemSize(void)
 {
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	TotalMaxReplicationSlots = max_replication_slots + max_repack_replication_slots;
+
+	if (TotalMaxReplicationSlots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(TotalMaxReplicationSlots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +214,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +228,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < TotalMaxReplicationSlots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +378,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +386,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +439,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = repack ? max_replication_slots : 0;
+	endpoint = repack ? TotalMaxReplicationSlots : max_replication_slots;
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +456,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -548,7 +561,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +589,7 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots + TotalMaxReplicationSlots);
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,7 +1676,11 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/*
+	 * FIXME how to relax this for repack in a way that doesn't mess
+	 * everything up?
+	 */
+	if (TotalMaxReplicationSlots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
 				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
@@ -2224,7 +2241,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (TotalMaxReplicationSlots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2249,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2354,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2455,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (TotalMaxReplicationSlots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2885,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2927,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..cdb4dbd87c9 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < TotalMaxReplicationSlots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < TotalMaxReplicationSlots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index e556b8844d8..8eb251659b0 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2c5e98d1d4d..9e9a390a01b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..88953576894 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,9 +324,13 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
+/* only for slotfuncs.c, slotsync.c etc */
+extern int TotalMaxReplicationSlots;
+
 /* shmem initialization functions */
 extern Size ReplicationSlotsShmemSize(void);
 extern void ReplicationSlotsShmemInit(void);
@@ -334,7 +338,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--brnevsqjnuzpyok4--





^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v51 09/10] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  3 +-
 src/backend/commands/repack_worker.c          |  4 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 80 +++++++++++--------
 src/backend/replication/slotfuncs.c           |  8 +-
 src/backend/replication/walsender.c           |  4 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/slot.h                |  3 +-
 12 files changed, 93 insertions(+), 48 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 422ba304982..a67dd6b9eb1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4638,6 +4638,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index bec18c44cc8..1424446ba7c 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index d4c1f0e7652..d932d526235 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3381,7 +3381,8 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+		/* FIXME rename to max_repack_processes? */
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index ff34e246469..610592a05b0 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -233,8 +233,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 09964198550..d83125afd0d 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index e75db69e3f6..28c89c5e10d 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -425,7 +425,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -814,6 +814,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1691,7 +1692,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index d553bd5dbff..2c6c6773ad2 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -152,6 +152,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -189,14 +191,15 @@ static void SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel);
 Size
 ReplicationSlotsShmemSize(void)
 {
+	int			totalslots = max_replication_slots + max_repack_replication_slots;
 	Size		size = 0;
 
-	if (max_replication_slots == 0)
+	if (totalslots == 0)
 		return size;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(totalslots, sizeof(ReplicationSlot)));
 
 	return size;
 }
@@ -209,7 +212,7 @@ ReplicationSlotsShmemInit(void)
 {
 	bool		found;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	ReplicationSlotCtl = (ReplicationSlotCtlData *)
@@ -223,7 +226,7 @@ ReplicationSlotsShmemInit(void)
 		/* First time through, so initialize */
 		MemSet(ReplicationSlotCtl, 0, ReplicationSlotsShmemSize());
 
-		for (i = 0; i < max_replication_slots; i++)
+		for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 		{
 			ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -373,6 +376,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -380,10 +384,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -432,12 +437,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -445,7 +454,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -455,7 +466,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -548,7 +560,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -576,7 +588,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -870,7 +883,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1252,7 +1265,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1307,7 +1320,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1374,12 +1387,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1454,11 +1467,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1515,13 +1528,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1618,11 +1631,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1663,10 +1676,12 @@ CheckSlotRequirements(void)
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	/* XXX we should be able to check exactly which type of slot we need */
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		ereport(ERROR,
 				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				 errmsg("replication slots can only be used if \"%s\" > 0 or \"%s\" > 0",
+						"max_replication_slots", "max_repack_replication_slots")));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2224,7 +2239,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2232,7 +2247,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2337,7 +2352,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2438,7 +2453,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
@@ -2868,7 +2883,7 @@ RestoreSlotFromDisk(const char *name)
 				 errhint("Change \"wal_level\" to be \"replica\" or higher.")));
 
 	/* nothing can be active yet, don't lock anything */
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot;
 
@@ -2910,6 +2925,7 @@ RestoreSlotFromDisk(const char *name)
 		break;
 	}
 
+	/* XXX might be misleading if the slots previously in use were REPACK. */
 	if (!restored)
 		ereport(FATAL,
 				(errmsg("too many replication slots active before shutdown"),
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..78dd3c4ea66 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -270,7 +270,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -665,7 +665,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index 2bb3f34dc6d..75ef3419a15 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1220,7 +1220,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1251,7 +1251,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fc0900efe5f..857be159f5c 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2070,6 +2070,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index c8194c27aa7..9c3c5d16361 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 4b4709f6e2c..c316a01a807 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,6 +324,7 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
@@ -334,7 +335,7 @@ extern void ReplicationSlotsShmemInit(void);
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
-- 
2.47.3


--r2slln3zpmilwu22
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v51-0010-CheckLogicalDecodingRequirements-be-specific-abo.patch"



^ permalink  raw  reply  [nested|flat] 403+ messages in thread

* [PATCH v56 2/3] Reserve replication slots specifically for REPACK
@ 2026-04-01 17:54 Álvaro Herrera <[email protected]>
  0 siblings, 0 replies; 403+ messages in thread

From: Álvaro Herrera @ 2026-04-01 17:54 UTC (permalink / raw)

This allows REPACK to not interfere with other operations that use
replication slots.  This eases configurability.
---
 doc/src/sgml/config.sgml                      | 16 ++++
 doc/src/sgml/ref/repack.sgml                  |  6 +-
 src/backend/commands/repack.c                 |  2 +-
 src/backend/commands/repack_worker.c          |  7 +-
 src/backend/replication/logical/launcher.c    |  2 +-
 src/backend/replication/logical/logical.c     |  8 +-
 .../replication/logical/logicalfuncs.c        |  2 +-
 src/backend/replication/logical/slotsync.c    |  5 +-
 src/backend/replication/slot.c                | 84 ++++++++++++-------
 src/backend/replication/slotfuncs.c           | 19 +++--
 src/backend/replication/walsender.c           |  9 +-
 src/backend/utils/misc/guc_parameters.dat     |  8 ++
 src/backend/utils/misc/postgresql.conf.sample |  2 +
 src/include/replication/logical.h             |  3 +-
 src/include/replication/slot.h                |  5 +-
 15 files changed, 116 insertions(+), 62 deletions(-)

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3324d2d3c49..3435732646e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -4639,6 +4639,22 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"'  # Windows
        </listitem>
       </varlistentry>
 
+      <varlistentry id="guc-max-repack-replication-slots" xreflabel="max_repack_replication_slots">
+       <term><varname>max_repack_replication_slots</varname> (<type>integer</type>)
+       <indexterm>
+        <primary><varname>max_repack_replication_slots</varname> configuration parameter</primary>
+       </indexterm>
+       </term>
+       <listitem>
+        <para>
+         Specifies the maximum number of replication slots for use of
+         the <command>REPACK</command> command.  The default is 5.
+         This parameter can only be set at server start.
+        </para>
+       </listitem>
+      </varlistentry>
+
+
       <varlistentry id="guc-max-replication-slots" xreflabel="max_replication_slots">
        <term><varname>max_replication_slots</varname> (<type>integer</type>)
        <indexterm>
diff --git a/doc/src/sgml/ref/repack.sgml b/doc/src/sgml/ref/repack.sgml
index e993dfb3108..c532a39ee07 100644
--- a/doc/src/sgml/ref/repack.sgml
+++ b/doc/src/sgml/ref/repack.sgml
@@ -293,9 +293,9 @@ REPACK [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] USING
 
        <listitem>
         <para>
-         The <link linkend="guc-max-replication-slots"><varname>max_replication_slots</varname></link>
-         configuration parameter does not allow for creation of an additional
-         replication slot.
+         The <link linkend="guc-max-repack-replication-slots"><varname>max_repack_replication_slots</varname></link>
+         configuration parameter does not allow for the creation of an
+         additional replication slot.
         </para>
        </listitem>
       </itemizedlist>
diff --git a/src/backend/commands/repack.c b/src/backend/commands/repack.c
index 17b639b3b44..5e97fcf3818 100644
--- a/src/backend/commands/repack.c
+++ b/src/backend/commands/repack.c
@@ -3357,7 +3357,7 @@ start_repack_decoding_worker(Oid relid)
 		ereport(ERROR,
 				errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				errmsg("out of background worker slots"),
-				errhint("You might need to increase \"%s\".", "max_worker_processes"));
+				errhint("You might need to increase \"%s\".", "max_repack_replication_slots"));
 
 	decoding_worker->seg = seg;
 	decoding_worker->error_mqh = mqh;
diff --git a/src/backend/commands/repack_worker.c b/src/backend/commands/repack_worker.c
index 94d034970b5..ea330310e27 100644
--- a/src/backend/commands/repack_worker.c
+++ b/src/backend/commands/repack_worker.c
@@ -212,7 +212,7 @@ repack_setup_logical_decoding(Oid relid)
 	 * Make sure we can use logical decoding.
 	 */
 	CheckSlotPermissions();
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(true);
 
 	/*
 	 * A single backend should not execute multiple REPACK commands at a time,
@@ -221,8 +221,8 @@ repack_setup_logical_decoding(Oid relid)
 	 * RS_TEMPORARY so that the slot gets cleaned up on ERROR.
 	 */
 	snprintf(NameStr(slotname), NAMEDATALEN, "repack_%d", MyProcPid);
-	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, false,
-						  false);
+	ReplicationSlotCreate(NameStr(slotname), true, RS_TEMPORARY, false, true,
+						  false, false);
 
 	EnsureLogicalDecodingEnabled();
 
@@ -233,6 +233,7 @@ repack_setup_logical_decoding(Oid relid)
 	ctx = CreateInitDecodingContext(REPL_PLUGIN_NAME,
 									NIL,
 									true,
+									true,
 									InvalidXLogRecPtr,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
diff --git a/src/backend/replication/logical/launcher.c b/src/backend/replication/logical/launcher.c
index 9e75a3e04ee..7adf4dbe0d1 100644
--- a/src/backend/replication/logical/launcher.c
+++ b/src/backend/replication/logical/launcher.c
@@ -1575,7 +1575,7 @@ CreateConflictDetectionSlot(void)
 			errmsg("creating replication conflict detection slot"));
 
 	ReplicationSlotCreate(CONFLICT_DETECTION_SLOT, false, RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	init_conflict_slot_xmin();
 }
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 8ceaf64d164..d8e02c53558 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -108,9 +108,9 @@ static void LoadOutputPlugin(OutputPluginCallbacks *callbacks, const char *plugi
  * decoding.
  */
 void
-CheckLogicalDecodingRequirements(void)
+CheckLogicalDecodingRequirements(bool repack)
 {
-	CheckSlotRequirements();
+	CheckSlotRequirements(repack);
 
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
@@ -304,6 +304,7 @@ StartupDecodingContext(List *output_plugin_options,
  * output_plugin_options -- contains options passed to the output plugin
  * need_full_snapshot -- if true, must obtain a snapshot able to read all
  *		tables; if false, one that can read only catalogs is acceptable.
+ * for_repack -- if true, we're going to be decoding for REPACK.
  * restart_lsn -- if given as invalid, it's this routine's responsibility to
  *		mark WAL as reserved by setting a convenient restart_lsn for the slot.
  *		Otherwise, we set for decoding to start from the given LSN without
@@ -324,6 +325,7 @@ LogicalDecodingContext *
 CreateInitDecodingContext(const char *plugin,
 						  List *output_plugin_options,
 						  bool need_full_snapshot,
+						  bool for_repack,
 						  XLogRecPtr restart_lsn,
 						  XLogReaderRoutine *xl_routine,
 						  LogicalOutputPluginWriterPrepareWrite prepare_write,
@@ -340,7 +342,7 @@ CreateInitDecodingContext(const char *plugin,
 	 * On a standby, this check is also required while creating the slot.
 	 * Check the comments in the function.
 	 */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(for_repack);
 
 	/* shorter lines... */
 	slot = MyReplicationSlot;
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 9760818941d..512013b0ef0 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -115,7 +115,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	if (PG_ARGISNULL(0))
 		ereport(ERROR,
diff --git a/src/backend/replication/logical/slotsync.c b/src/backend/replication/logical/slotsync.c
index 8b53bd3ac7f..ae900f13467 100644
--- a/src/backend/replication/logical/slotsync.c
+++ b/src/backend/replication/logical/slotsync.c
@@ -434,7 +434,7 @@ get_local_synced_slots(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -823,6 +823,7 @@ synchronize_one_slot(RemoteSlot *remote_slot, Oid remote_dbid,
 		 */
 		ReplicationSlotCreate(remote_slot->name, true, RS_TEMPORARY,
 							  remote_slot->two_phase,
+							  false,
 							  remote_slot->failover,
 							  true);
 
@@ -1707,7 +1708,7 @@ update_synced_slots_inactive_since(void)
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index a1f37e59dbc..e6722fc0212 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -160,6 +160,8 @@ ReplicationSlot *MyReplicationSlot = NULL;
 /* GUC variables */
 int			max_replication_slots = 10; /* the maximum number of replication
 										 * slots */
+int			max_repack_replication_slots = 5;	/* the maximum number of slots
+												 * for REPACK */
 
 /*
  * Invalidate replication slots that have remained idle longer than this
@@ -199,12 +201,13 @@ ReplicationSlotsShmemRequest(void *arg)
 {
 	Size		size;
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots + max_repack_replication_slots == 0)
 		return;
 
 	size = offsetof(ReplicationSlotCtlData, replication_slots);
 	size = add_size(size,
-					mul_size(max_replication_slots, sizeof(ReplicationSlot)));
+					mul_size(max_replication_slots + max_repack_replication_slots,
+							 sizeof(ReplicationSlot)));
 	ShmemRequestStruct(.name = "ReplicationSlot Ctl",
 					   .size = size,
 					   .ptr = (void **) &ReplicationSlotCtl,
@@ -217,7 +220,7 @@ ReplicationSlotsShmemRequest(void *arg)
 static void
 ReplicationSlotsShmemInit(void *arg)
 {
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[i];
 
@@ -366,6 +369,7 @@ IsSlotForConflictCheck(const char *name)
  * db_specific: logical decoding is db specific; if the slot is going to
  *	   be used for that pass true, otherwise false.
  * two_phase: If enabled, allows decoding of prepared transactions.
+ * repack: If true, use a slot from the pool for REPACK.
  * failover: If enabled, allows the slot to be synced to standbys so
  *     that logical replication can be resumed after failover.
  * synced: True if the slot is synchronized from the primary server.
@@ -373,10 +377,11 @@ IsSlotForConflictCheck(const char *name)
 void
 ReplicationSlotCreate(const char *name, bool db_specific,
 					  ReplicationSlotPersistency persistency,
-					  bool two_phase, bool failover, bool synced)
+					  bool two_phase, bool repack, bool failover, bool synced)
 {
 	ReplicationSlot *slot = NULL;
-	int			i;
+	int			startpoint,
+				endpoint;
 
 	Assert(MyReplicationSlot == NULL);
 
@@ -425,12 +430,16 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_EXCLUSIVE);
 
 	/*
-	 * Check for name collision, and identify an allocatable slot.  We need to
-	 * hold ReplicationSlotControlLock in shared mode for this, so that nobody
-	 * else can change the in_use flags while we're looking at them.
+	 * Check for name collision (across the whole array), and identify an
+	 * allocatable slot (in the array slice specific to our current use case:
+	 * either general, or REPACK only).  We need to hold
+	 * ReplicationSlotControlLock in shared mode for this, so that nobody else
+	 * can change the in_use flags while we're looking at them.
 	 */
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	startpoint = !repack ? 0 : max_replication_slots;
+	endpoint = max_replication_slots + (repack ? max_repack_replication_slots : 0);
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -438,7 +447,9 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 			ereport(ERROR,
 					(errcode(ERRCODE_DUPLICATE_OBJECT),
 					 errmsg("replication slot \"%s\" already exists", name)));
-		if (!s->in_use && slot == NULL)
+
+		if (i >= startpoint && i < endpoint &&
+			!s->in_use && slot == NULL)
 			slot = s;
 	}
 	LWLockRelease(ReplicationSlotControlLock);
@@ -448,7 +459,8 @@ ReplicationSlotCreate(const char *name, bool db_specific,
 		ereport(ERROR,
 				(errcode(ERRCODE_CONFIGURATION_LIMIT_EXCEEDED),
 				 errmsg("all replication slots are in use"),
-				 errhint("Free one or increase \"max_replication_slots\".")));
+				 errhint("Free one or increase \"%s\".",
+						 repack ? "max_repack_replication_slots" : "max_replication_slots")));
 
 	/*
 	 * Since this slot is not in use, nobody should be looking at any part of
@@ -541,7 +553,7 @@ SearchNamedReplicationSlot(const char *name, bool need_lock)
 	if (need_lock)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -569,7 +581,8 @@ int
 ReplicationSlotIndex(ReplicationSlot *slot)
 {
 	Assert(slot >= ReplicationSlotCtl->replication_slots &&
-		   slot < ReplicationSlotCtl->replication_slots + max_replication_slots);
+		   slot < ReplicationSlotCtl->replication_slots +
+		   (max_replication_slots + max_repack_replication_slots));
 
 	return slot - ReplicationSlotCtl->replication_slots;
 }
@@ -863,7 +876,7 @@ ReplicationSlotCleanup(bool synced_only)
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
@@ -1245,7 +1258,7 @@ ReplicationSlotsComputeRequiredXmin(bool already_locked)
 	if (!already_locked)
 		LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		TransactionId effective_xmin;
@@ -1300,7 +1313,7 @@ ReplicationSlotsComputeRequiredLSN(void)
 	Assert(ReplicationSlotCtl != NULL);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		XLogRecPtr	restart_lsn;
@@ -1367,12 +1380,12 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
 	XLogRecPtr	result = InvalidXLogRecPtr;
 	int			i;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return InvalidXLogRecPtr;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		XLogRecPtr	restart_lsn;
@@ -1447,11 +1460,11 @@ ReplicationSlotsCountDBSlots(Oid dboid, int *nslots, int *nactive)
 
 	*nslots = *nactive = 0;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 
@@ -1508,13 +1521,13 @@ ReplicationSlotsDropDBSlots(Oid dboid)
 	bool		found_valid_logicalslot;
 	bool		dropped = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		char	   *slotname;
@@ -1611,11 +1624,11 @@ CheckLogicalSlotExists(void)
 {
 	bool		found = false;
 
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return false;
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s;
 		bool		invalidated;
@@ -1649,17 +1662,24 @@ CheckLogicalSlotExists(void)
  * slots.
  */
 void
-CheckSlotRequirements(void)
+CheckSlotRequirements(bool repack)
 {
 	/*
 	 * NB: Adding a new requirement likely means that RestoreSlotFromDisk()
 	 * needs the same check.
 	 */
 
-	if (max_replication_slots == 0)
+	if (!repack && max_replication_slots == 0)
 		ereport(ERROR,
-				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
-				 errmsg("replication slots can only be used if \"max_replication_slots\" > 0")));
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("replication slots can only be used if \"%s\" > 0",
+					   "max_replication_slots"));
+
+	if (repack && max_repack_replication_slots == 0)
+		ereport(ERROR,
+				errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				errmsg("REPACK can only be used if \"%s\" > 0",
+					   "max_repack_replication_slots"));
 
 	if (wal_level < WAL_LEVEL_REPLICA)
 		ereport(ERROR,
@@ -2210,7 +2230,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 	Assert(!(possible_causes & RS_INVAL_WAL_REMOVED) || oldestSegno > 0);
 	Assert(possible_causes != RS_INVAL_NONE);
 
-	if (max_replication_slots == 0)
+	if (max_replication_slots == 0 && max_repack_replication_slots == 0)
 		return invalidated;
 
 	XLogSegNoOffsetToRecPtr(oldestSegno, 0, wal_segment_size, oldestLSN);
@@ -2218,7 +2238,7 @@ InvalidateObsoleteReplicationSlots(uint32 possible_causes,
 restart:
 	found_valid_logicalslot = false;
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		bool		released_lock = false;
@@ -2323,7 +2343,7 @@ CheckPointReplicationSlots(bool is_shutdown)
 	 */
 	LWLockAcquire(ReplicationSlotAllocationLock, LW_SHARED);
 
-	for (i = 0; i < max_replication_slots; i++)
+	for (i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 		char		path[MAXPGPATH];
@@ -2424,7 +2444,7 @@ StartupReplicationSlots(void)
 	FreeDir(replication_dir);
 
 	/* currently no slots exist, we're done. */
-	if (max_replication_slots <= 0)
+	if (max_replication_slots + max_repack_replication_slots <= 0)
 		return;
 
 	/* Now that we have recovered all the data, compute replication xmin */
diff --git a/src/backend/replication/slotfuncs.c b/src/backend/replication/slotfuncs.c
index 9f5e4f998fe..16fbd383735 100644
--- a/src/backend/replication/slotfuncs.c
+++ b/src/backend/replication/slotfuncs.c
@@ -53,7 +53,7 @@ create_physical_replication_slot(char *name, bool immediately_reserve,
 	/* acquire replication slot, this will check for conflicting names */
 	ReplicationSlotCreate(name, false,
 						  temporary ? RS_TEMPORARY : RS_PERSISTENT, false,
-						  false, false);
+						  false, false, false);
 
 	if (immediately_reserve)
 	{
@@ -90,7 +90,7 @@ pg_create_physical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	create_physical_replication_slot(NameStr(*name),
 									 immediately_reserve,
@@ -146,7 +146,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ReplicationSlotCreate(name, true,
 						  temporary ? RS_TEMPORARY : RS_EPHEMERAL, two_phase,
-						  failover, false);
+						  false, failover, false);
 
 	/*
 	 * Ensure the logical decoding is enabled before initializing the logical
@@ -164,6 +164,7 @@ create_logical_replication_slot(char *name, char *plugin,
 	 */
 	ctx = CreateInitDecodingContext(plugin, NIL,
 									false,	/* just catalogs is OK */
+									false,	/* not repack */
 									restart_lsn,
 									XL_ROUTINE(.page_read = read_local_xlog_page,
 											   .segment_open = wal_segment_open,
@@ -203,7 +204,7 @@ pg_create_logical_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	create_logical_replication_slot(NameStr(*name),
 									NameStr(*plugin),
@@ -240,7 +241,7 @@ pg_drop_replication_slot(PG_FUNCTION_ARGS)
 
 	CheckSlotPermissions();
 
-	CheckSlotRequirements();
+	CheckSlotRequirements(false);
 
 	ReplicationSlotDrop(NameStr(*name), true);
 
@@ -270,7 +271,7 @@ pg_get_replication_slots(PG_FUNCTION_ARGS)
 	currlsn = GetXLogWriteRecPtr();
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
-	for (slotno = 0; slotno < max_replication_slots; slotno++)
+	for (slotno = 0; slotno < max_replication_slots + max_repack_replication_slots; slotno++)
 	{
 		ReplicationSlot *slot = &ReplicationSlotCtl->replication_slots[slotno];
 		ReplicationSlot slot_contents;
@@ -648,9 +649,9 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	CheckSlotPermissions();
 
 	if (logical_slot)
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 	else
-		CheckSlotRequirements();
+		CheckSlotRequirements(false);
 
 	LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
 
@@ -665,7 +666,7 @@ copy_replication_slot(FunctionCallInfo fcinfo, bool logical_slot)
 	 * managed to create the new slot, we advance the new slot's restart_lsn
 	 * to the source slot's updated restart_lsn the second time we lock it.
 	 */
-	for (int i = 0; i < max_replication_slots; i++)
+	for (int i = 0; i < max_replication_slots + max_repack_replication_slots; i++)
 	{
 		ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index b4a2117a7f9..bad45adb004 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1241,7 +1241,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 	{
 		ReplicationSlotCreate(cmd->slotname, false,
 							  cmd->temporary ? RS_TEMPORARY : RS_PERSISTENT,
-							  false, false, false);
+							  false, false, false, false);
 
 		if (reserve_wal)
 		{
@@ -1261,7 +1261,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 
 		Assert(cmd->kind == REPLICATION_KIND_LOGICAL);
 
-		CheckLogicalDecodingRequirements();
+		CheckLogicalDecodingRequirements(false);
 
 		/*
 		 * Initially create persistent slot as ephemeral - that allows us to
@@ -1272,7 +1272,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		 */
 		ReplicationSlotCreate(cmd->slotname, true,
 							  cmd->temporary ? RS_TEMPORARY : RS_EPHEMERAL,
-							  two_phase, failover, false);
+							  two_phase, false, failover, false);
 
 		/*
 		 * Do options check early so that we can bail before calling the
@@ -1330,6 +1330,7 @@ CreateReplicationSlot(CreateReplicationSlotCmd *cmd)
 		Assert(IsLogicalDecodingEnabled());
 
 		ctx = CreateInitDecodingContext(cmd->plugin, NIL, need_full_snapshot,
+										false,
 										InvalidXLogRecPtr,
 										XL_ROUTINE(.page_read = logical_read_xlog_page,
 												   .segment_open = WalSndSegmentOpen,
@@ -1487,7 +1488,7 @@ StartLogicalReplication(StartReplicationCmd *cmd)
 	QueryCompletion qc;
 
 	/* make sure that our requirements are still fulfilled */
-	CheckLogicalDecodingRequirements();
+	CheckLogicalDecodingRequirements(false);
 
 	Assert(!MyReplicationSlot);
 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index fcb6ab80583..632f3ba4989 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -2079,6 +2079,14 @@
   max => 'MAX_BACKENDS',
 },
 
+{ name => 'max_repack_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
+  short_desc => 'Sets the maximum number of replication slots for use by REPACK.',
+  variable => 'max_repack_replication_slots',
+  boot_val => '5',
+  min => '0',
+  max => 'MAX_BACKENDS',
+},
+
 /* see max_wal_senders */
 { name => 'max_replication_slots', type => 'int', context => 'PGC_POSTMASTER', group => 'REPLICATION_SENDING',
   short_desc => 'Sets the maximum number of simultaneously defined replication slots.',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index e3e462f3efb..2e10eb4a36a 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -348,6 +348,8 @@
                                 # (change requires restart)
 #max_replication_slots = 10     # max number of replication slots
                                 # (change requires restart)
+#max_repack_replication_slots = 5 # max number of replication slots for REPACK
+                                # (change requires restart)
 #wal_keep_size = 0              # in megabytes; 0 disables
 #max_slot_wal_keep_size = -1    # in megabytes; -1 disables
 #idle_replication_slot_timeout = 0      # in seconds; 0 disables
diff --git a/src/include/replication/logical.h b/src/include/replication/logical.h
index bc9d4ece672..bc075b16741 100644
--- a/src/include/replication/logical.h
+++ b/src/include/replication/logical.h
@@ -115,11 +115,12 @@ typedef struct LogicalDecodingContext
 } LogicalDecodingContext;
 
 
-extern void CheckLogicalDecodingRequirements(void);
+extern void CheckLogicalDecodingRequirements(bool repack);
 
 extern LogicalDecodingContext *CreateInitDecodingContext(const char *plugin,
 														 List *output_plugin_options,
 														 bool need_full_snapshot,
+														 bool for_repack,
 														 XLogRecPtr restart_lsn,
 														 XLogReaderRoutine *xl_routine,
 														 LogicalOutputPluginWriterPrepareWrite prepare_write,
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index 1a3557de607..77c8d0975b6 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -324,13 +324,14 @@ extern PGDLLIMPORT ReplicationSlot *MyReplicationSlot;
 
 /* GUCs */
 extern PGDLLIMPORT int max_replication_slots;
+extern PGDLLIMPORT int max_repack_replication_slots;
 extern PGDLLIMPORT char *synchronized_standby_slots;
 extern PGDLLIMPORT int idle_replication_slot_timeout_secs;
 
 /* management of individual slots */
 extern void ReplicationSlotCreate(const char *name, bool db_specific,
 								  ReplicationSlotPersistency persistency,
-								  bool two_phase, bool failover,
+								  bool two_phase, bool repack, bool failover,
 								  bool synced);
 extern void ReplicationSlotPersist(void);
 extern void ReplicationSlotDrop(const char *name, bool nowait);
@@ -373,7 +374,7 @@ extern void ReplicationSlotDropAtPubNode(WalReceiverConn *wrconn, char *slotname
 extern void StartupReplicationSlots(void);
 extern void CheckPointReplicationSlots(bool is_shutdown);
 
-extern void CheckSlotRequirements(void);
+extern void CheckSlotRequirements(bool repack);
 extern void CheckSlotPermissions(void);
 extern ReplicationSlotInvalidationCause
 			GetSlotInvalidationCause(const char *cause_name);
-- 
2.47.3


--qs77q6fpwolne4ds
Content-Type: text/x-diff; charset=utf-8
Content-Disposition: attachment;
	filename="v56-0003-Error-out-any-process-that-would-block-at-REPACK.patch"



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