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[PATCH v2 1/3] rework locking code in GetMultiXactIdMembers 2+ messages / 1 participants [nested] [flat]
* [PATCH v2 1/3] rework locking code in GetMultiXactIdMembers @ 2024-03-03 14:20 Alvaro Herrera <[email protected]> 0 siblings, 0 replies; 2+ messages in thread From: Alvaro Herrera @ 2024-03-03 14:20 UTC (permalink / raw) Per Coverity --- src/backend/access/transam/multixact.c | 53 +++++++++++--------------- 1 file changed, 22 insertions(+), 31 deletions(-) diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index cd476b94fa..83b578dced 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -1247,14 +1247,12 @@ GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members, MultiXactOffset offset; int length; int truelength; - int i; MultiXactId oldestMXact; MultiXactId nextMXact; MultiXactId tmpMXact; MultiXactOffset nextOffset; MultiXactMember *ptr; LWLock *lock; - LWLock *prevlock = NULL; debug_elog3(DEBUG2, "GetMembers: asked for %u", multi); @@ -1361,18 +1359,9 @@ retry: pageno = MultiXactIdToOffsetPage(multi); entryno = MultiXactIdToOffsetEntry(multi); - /* - * If this page falls under a different bank, release the old bank's lock - * and acquire the lock of the new bank. - */ + /* Acquire the bank lock for the page we need. */ lock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); - if (lock != prevlock) - { - if (prevlock != NULL) - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; - } + LWLockAcquire(lock, LW_EXCLUSIVE); slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi); offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno]; @@ -1407,17 +1396,19 @@ retry: if (pageno != prev_pageno) { + LWLock *newlock; + /* * Since we're going to access a different SLRU page, if this page * falls under a different bank, release the old bank's lock and * acquire the lock of the new bank. */ - lock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); - if (prevlock != lock) + newlock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); + if (newlock != lock) { - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; + LWLockRelease(lock); + LWLockAcquire(newlock, LW_EXCLUSIVE); + lock = newlock; } slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact); } @@ -1429,8 +1420,7 @@ retry: if (nextMXOffset == 0) { /* Corner case 2: next multixact is still being filled in */ - LWLockRelease(prevlock); - prevlock = NULL; + LWLockRelease(lock); CHECK_FOR_INTERRUPTS(); pg_usleep(1000L); goto retry; @@ -1439,14 +1429,14 @@ retry: length = nextMXOffset - offset; } - LWLockRelease(prevlock); - prevlock = NULL; + LWLockRelease(lock); + lock = NULL; ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember)); truelength = 0; prev_pageno = -1; - for (i = 0; i < length; i++, offset++) + for (int i = 0; i < length; i++, offset++) { TransactionId *xactptr; uint32 *flagsptr; @@ -1459,18 +1449,20 @@ retry: if (pageno != prev_pageno) { + LWLock *newlock; + /* * Since we're going to access a different SLRU page, if this page * falls under a different bank, release the old bank's lock and * acquire the lock of the new bank. */ - lock = SimpleLruGetBankLock(MultiXactMemberCtl, pageno); - if (lock != prevlock) + newlock = SimpleLruGetBankLock(MultiXactMemberCtl, pageno); + if (newlock != lock) { - if (prevlock) - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; + if (lock) + LWLockRelease(lock); + LWLockAcquire(newlock, LW_EXCLUSIVE); + lock = newlock; } slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi); @@ -1496,8 +1488,7 @@ retry: truelength++; } - if (prevlock) - LWLockRelease(prevlock); + LWLockRelease(lock); /* A multixid with zero members should not happen */ Assert(truelength > 0); -- 2.39.2 --gflnge3qfnp343ni Content-Type: text/x-diff; charset=utf-8 Content-Disposition: attachment; filename="v2-0002-Rework-redundant-loop-in-subtrans.c.patch" ^ permalink raw reply [nested|flat] 2+ messages in thread
* [PATCH] rework locking code in GetMultiXactIdMembers @ 2024-03-03 14:20 Alvaro Herrera <[email protected]> 0 siblings, 0 replies; 2+ messages in thread From: Alvaro Herrera @ 2024-03-03 14:20 UTC (permalink / raw) Per Coverity --- src/backend/access/transam/multixact.c | 52 ++++++++++---------------- 1 file changed, 20 insertions(+), 32 deletions(-) diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 9b81506145..ec446949a9 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -1250,14 +1250,12 @@ GetMultiXactIdMembers(MultiXactId multi, MultiXactMember **members, MultiXactOffset offset; int length; int truelength; - int i; MultiXactId oldestMXact; MultiXactId nextMXact; MultiXactId tmpMXact; MultiXactOffset nextOffset; MultiXactMember *ptr; LWLock *lock; - LWLock *prevlock = NULL; debug_elog3(DEBUG2, "GetMembers: asked for %u", multi); @@ -1364,18 +1362,9 @@ retry: pageno = MultiXactIdToOffsetPage(multi); entryno = MultiXactIdToOffsetEntry(multi); - /* - * If this page falls under a different bank, release the old bank's lock - * and acquire the lock of the new bank. - */ + /* Acquire the bank lock for the page we need. */ lock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); - if (lock != prevlock) - { - if (prevlock != NULL) - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; - } + LWLockAcquire(lock, LW_EXCLUSIVE); slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, multi); offptr = (MultiXactOffset *) MultiXactOffsetCtl->shared->page_buffer[slotno]; @@ -1410,17 +1399,19 @@ retry: if (pageno != prev_pageno) { + LWLock *newlock; + /* * Since we're going to access a different SLRU page, if this page * falls under a different bank, release the old bank's lock and * acquire the lock of the new bank. */ - lock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); - if (prevlock != lock) + newlock = SimpleLruGetBankLock(MultiXactOffsetCtl, pageno); + if (newlock != lock) { - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; + LWLockRelease(lock); + LWLockAcquire(newlock, LW_EXCLUSIVE); + lock = newlock; } slotno = SimpleLruReadPage(MultiXactOffsetCtl, pageno, true, tmpMXact); } @@ -1432,8 +1423,8 @@ retry: if (nextMXOffset == 0) { /* Corner case 2: next multixact is still being filled in */ - LWLockRelease(prevlock); - prevlock = NULL; + LWLockRelease(lock); + lock = NULL; CHECK_FOR_INTERRUPTS(); pg_usleep(1000L); goto retry; @@ -1442,14 +1433,11 @@ retry: length = nextMXOffset - offset; } - LWLockRelease(prevlock); - prevlock = NULL; - ptr = (MultiXactMember *) palloc(length * sizeof(MultiXactMember)); truelength = 0; prev_pageno = -1; - for (i = 0; i < length; i++, offset++) + for (int i = 0; i < length; i++, offset++) { TransactionId *xactptr; uint32 *flagsptr; @@ -1462,18 +1450,19 @@ retry: if (pageno != prev_pageno) { + LWLock *newlock; + /* * Since we're going to access a different SLRU page, if this page * falls under a different bank, release the old bank's lock and * acquire the lock of the new bank. */ - lock = SimpleLruGetBankLock(MultiXactMemberCtl, pageno); - if (lock != prevlock) + newlock = SimpleLruGetBankLock(MultiXactMemberCtl, pageno); + if (newlock != lock) { - if (prevlock) - LWLockRelease(prevlock); - LWLockAcquire(lock, LW_EXCLUSIVE); - prevlock = lock; + LWLockRelease(lock); + LWLockAcquire(newlock, LW_EXCLUSIVE); + lock = newlock; } slotno = SimpleLruReadPage(MultiXactMemberCtl, pageno, true, multi); @@ -1499,8 +1488,7 @@ retry: truelength++; } - if (prevlock) - LWLockRelease(prevlock); + LWLockRelease(lock); /* A multixid with zero members should not happen */ Assert(truelength > 0); -- 2.39.2 --rb5vb6debo3bx6lt-- ^ permalink raw reply [nested|flat] 2+ messages in thread
end of thread, other threads:[~2024-03-03 14:20 UTC | newest] Thread overview: 2+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2024-03-03 14:20 [PATCH v2 1/3] rework locking code in GetMultiXactIdMembers Alvaro Herrera <[email protected]> 2024-03-03 14:20 [PATCH] rework locking code in GetMultiXactIdMembers Alvaro Herrera <[email protected]>
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