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| author | Nathan Bossart <nathan@postgresql.org> | 2024-02-29 14:34:10 -0600 |
|---|---|---|
| committer | Nathan Bossart <nathan@postgresql.org> | 2024-02-29 14:34:10 -0600 |
| commit | 963d3072af21afbcb1183b3c960135cc7df02f3f (patch) | |
| tree | 95f67624ab4f71c046ca0dcd4afd22a22624c714 /src/backend/access/transam/xlog.c | |
| parent | 3179701505b9ec58243ffba9d22b1803f320bf60 (diff) | |
| download | postgresql-963d3072af21afbcb1183b3c960135cc7df02f3f.tar.gz postgresql-963d3072af21afbcb1183b3c960135cc7df02f3f.zip | |
Convert unloggedLSN to an atomic variable.
Currently, this variable is an XLogRecPtr protected by a spinlock.
By converting it to an atomic variable, we can remove the spinlock,
which saves a small amount of shared memory space. Since this code
is not performance-critical, we use atomic operations with full
barrier semantics to make it easy to reason about correctness.
Author: John Morris
Reviewed-by: Michael Paquier, Robert Haas, Andres Freund, Stephen Frost, Bharath Rupireddy
Discussion: https://postgr.es/m/BYAPR13MB26772534335255E50318C574A0409%40BYAPR13MB2677.namprd13.prod.outlook.com
Discussion: https://postgr.es/m/MN2PR13MB2688FD8B757316CB5C54C8A2A0DDA%40MN2PR13MB2688.namprd13.prod.outlook.com
Diffstat (limited to 'src/backend/access/transam/xlog.c')
| -rw-r--r-- | src/backend/access/transam/xlog.c | 26 |
1 files changed, 9 insertions, 17 deletions
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index c1162d55bff..eb02e3b6a6f 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -470,9 +470,8 @@ typedef struct XLogCtlData XLogSegNo lastRemovedSegNo; /* latest removed/recycled XLOG segment */ - /* Fake LSN counter, for unlogged relations. Protected by ulsn_lck. */ - XLogRecPtr unloggedLSN; - slock_t ulsn_lck; + /* Fake LSN counter, for unlogged relations. */ + pg_atomic_uint64 unloggedLSN; /* Time and LSN of last xlog segment switch. Protected by WALWriteLock. */ pg_time_t lastSegSwitchTime; @@ -4498,14 +4497,7 @@ DataChecksumsEnabled(void) XLogRecPtr GetFakeLSNForUnloggedRel(void) { - XLogRecPtr nextUnloggedLSN; - - /* increment the unloggedLSN counter, need SpinLock */ - SpinLockAcquire(&XLogCtl->ulsn_lck); - nextUnloggedLSN = XLogCtl->unloggedLSN++; - SpinLockRelease(&XLogCtl->ulsn_lck); - - return nextUnloggedLSN; + return pg_atomic_fetch_add_u64(&XLogCtl->unloggedLSN, 1); } /* @@ -4921,7 +4913,7 @@ XLOGShmemInit(void) SpinLockInit(&XLogCtl->Insert.insertpos_lck); SpinLockInit(&XLogCtl->info_lck); - SpinLockInit(&XLogCtl->ulsn_lck); + pg_atomic_init_u64(&XLogCtl->unloggedLSN, InvalidXLogRecPtr); } /* @@ -5526,9 +5518,11 @@ StartupXLOG(void) * the unlogged LSN counter can be reset too. */ if (ControlFile->state == DB_SHUTDOWNED) - XLogCtl->unloggedLSN = ControlFile->unloggedLSN; + pg_atomic_write_membarrier_u64(&XLogCtl->unloggedLSN, + ControlFile->unloggedLSN); else - XLogCtl->unloggedLSN = FirstNormalUnloggedLSN; + pg_atomic_write_membarrier_u64(&XLogCtl->unloggedLSN, + FirstNormalUnloggedLSN); /* * Copy any missing timeline history files between 'now' and the recovery @@ -7110,9 +7104,7 @@ CreateCheckPoint(int flags) * unused on non-shutdown checkpoints, but seems useful to store it always * for debugging purposes. */ - SpinLockAcquire(&XLogCtl->ulsn_lck); - ControlFile->unloggedLSN = XLogCtl->unloggedLSN; - SpinLockRelease(&XLogCtl->ulsn_lck); + ControlFile->unloggedLSN = pg_atomic_read_membarrier_u64(&XLogCtl->unloggedLSN); UpdateControlFile(); LWLockRelease(ControlFileLock); |