From 0e7ac0c8ae5f7d151412fb61ba582394e60271cf Mon Sep 17 00:00:00 2001 From: Thomas Munro Date: Thu, 27 Oct 2022 12:40:12 +1300 Subject: [PATCH v2 6/9] Use SetLatches() for SERIALIZABLE DEFERRABLE wakeups. Don't issue SetLatch()'s system call while holding a highly contended LWLock. Collect them in a LatchBatch to be set after the lock is released. Once woken, other backends will immediately try to acquire that lock anyway so it's better to wake after releasing. Take this opportunity to retire the confusingly named ProcSendSignal() and replace it with something that gives the latch pointer we need. There was only one other caller, in bufmgr.c, which is easily changed. Discussion: https://postgr.es/m/CA%2BhUKGKmO7ze0Z6WXKdrLxmvYa%3DzVGGXOO30MMktufofVwEm1A%40mail.gmail.com --- src/backend/storage/buffer/bufmgr.c | 2 +- src/backend/storage/ipc/procsignal.c | 2 -- src/backend/storage/lmgr/predicate.c | 5 ++++- src/backend/storage/lmgr/proc.c | 12 ------------ src/include/storage/proc.h | 4 +++- 5 files changed, 8 insertions(+), 17 deletions(-) diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index 73d30bf619..df15f5e6c2 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -1918,7 +1918,7 @@ UnpinBuffer(BufferDesc *buf) buf_state &= ~BM_PIN_COUNT_WAITER; UnlockBufHdr(buf, buf_state); - ProcSendSignal(wait_backend_pgprocno); + SetLatch(GetProcLatchByNumber(wait_backend_pgprocno)); } else UnlockBufHdr(buf, buf_state); diff --git a/src/backend/storage/ipc/procsignal.c b/src/backend/storage/ipc/procsignal.c index 7767657f27..280e4b91dd 100644 --- a/src/backend/storage/ipc/procsignal.c +++ b/src/backend/storage/ipc/procsignal.c @@ -254,8 +254,6 @@ CleanupProcSignalState(int status, Datum arg) * * On success (a signal was sent), zero is returned. * On error, -1 is returned, and errno is set (typically to ESRCH or EPERM). - * - * Not to be confused with ProcSendSignal */ int SendProcSignal(pid_t pid, ProcSignalReason reason, BackendId backendId) diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c index e8120174d6..c62adea6b3 100644 --- a/src/backend/storage/lmgr/predicate.c +++ b/src/backend/storage/lmgr/predicate.c @@ -3339,6 +3339,7 @@ ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe) nextConflict, possibleUnsafeConflict; SERIALIZABLEXACT *roXact; + LatchGroup wakeups = {0}; /* * We can't trust XactReadOnly here, because a transaction which started @@ -3672,7 +3673,7 @@ ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe) */ if (SxactIsDeferrableWaiting(roXact) && (SxactIsROUnsafe(roXact) || SxactIsROSafe(roXact))) - ProcSendSignal(roXact->pgprocno); + AddLatch(&wakeups, GetProcLatchByNumber(roXact->pgprocno)); possibleUnsafeConflict = nextConflict; } @@ -3698,6 +3699,8 @@ ReleasePredicateLocks(bool isCommit, bool isReadOnlySafe) LWLockRelease(SerializableXactHashLock); + SetLatches(&wakeups); + LWLockAcquire(SerializableFinishedListLock, LW_EXCLUSIVE); /* Add this to the list of transactions to check for later cleanup. */ diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 281260dab3..48f962e6bd 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -1890,18 +1890,6 @@ ProcWaitForSignal(uint32 wait_event_info) CHECK_FOR_INTERRUPTS(); } -/* - * ProcSendSignal - set the latch of a backend identified by pgprocno - */ -void -ProcSendSignal(int pgprocno) -{ - if (pgprocno < 0 || pgprocno >= ProcGlobal->allProcCount) - elog(ERROR, "pgprocno out of range"); - - SetLatch(&ProcGlobal->allProcs[pgprocno].procLatch); -} - /* * BecomeLockGroupLeader - designate process as lock group leader * diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 0ae47325e4..ab17cb66b8 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -413,6 +413,9 @@ extern PGDLLIMPORT PGPROC *PreparedXactProcs; /* Accessor for PGPROC given a pgprocno. */ #define GetPGProcByNumber(n) (&ProcGlobal->allProcs[(n)]) +/* Accessor for procLatch given a pgprocno. */ +#define GetProcLatchByNumber(n) (&(GetPGProcByNumber(n))->procLatch) + /* * We set aside some extra PGPROC structures for auxiliary processes, * ie things that aren't full-fledged backends but need shmem access. @@ -456,7 +459,6 @@ extern bool IsWaitingForLock(void); extern void LockErrorCleanup(void); extern void ProcWaitForSignal(uint32 wait_event_info); -extern void ProcSendSignal(int pgprocno); extern PGPROC *AuxiliaryPidGetProc(int pid); -- 2.37.0 (Apple Git-136)