From b3d1478d1ac0c0df6c36b0cd097d23b9b77d4243 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Mon, 18 Jan 2021 13:14:39 -0500 Subject: [PATCH v1] Remove CheckpointLock. Up until now, we've held this lock when performing a checkpoint or restartpoint, but this isn't actually necessary, because only one process can be performing a checkpoint at a time: either the checkpointer, during normal operation, or the postmaster, during single-user operation. So, we don't need the lock. One possible concern in making this change is that it means that a substantial amount of code where HOLD_INTERRUPTS() was previously in effect due to the preceding LWLockAcquire() would now be running without that. This could mean that ProcessInterrupts() gets called in places from which it didn't before. However, this seems unlikely to do very much, because the checkpointer doesn't have any signal mapped to die(), so it's not clear how, for example, ProcDiePending = true could happen in the first place. Similarly with ClientConnectionLost and recovery conflicts. --- doc/src/sgml/monitoring.sgml | 4 ---- src/backend/access/heap/rewriteheap.c | 4 ++-- src/backend/access/transam/xlog.c | 28 +----------------------- src/backend/replication/logical/origin.c | 4 ++-- src/backend/storage/lmgr/lwlocknames.txt | 2 +- 5 files changed, 6 insertions(+), 36 deletions(-) diff --git a/doc/src/sgml/monitoring.sgml b/doc/src/sgml/monitoring.sgml index f05140dd42..9496f76b1f 100644 --- a/doc/src/sgml/monitoring.sgml +++ b/doc/src/sgml/monitoring.sgml @@ -1880,10 +1880,6 @@ postgres 27093 0.0 0.0 30096 2752 ? Ss 11:34 0:00 postgres: ser Waiting to associate a data block with a buffer in the buffer pool. - - Checkpoint - Waiting to begin a checkpoint. - CheckpointerComm Waiting to manage fsync requests. diff --git a/src/backend/access/heap/rewriteheap.c b/src/backend/access/heap/rewriteheap.c index 29ffe40670..fcaad9ba0b 100644 --- a/src/backend/access/heap/rewriteheap.c +++ b/src/backend/access/heap/rewriteheap.c @@ -1256,8 +1256,8 @@ CheckPointLogicalRewriteHeap(void) /* * The file cannot vanish due to concurrency since this function - * is the only one removing logical mappings and it's run while - * CheckpointLock is held exclusively. + * is the only one removing logical mappings and only one + * checkpoint can be in progress at a time. */ if (fd < 0) ereport(ERROR, diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index 470e113b33..cc007b8963 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -430,10 +430,6 @@ static XLogRecPtr RedoStartLSN = InvalidXLogRecPtr; * ControlFileLock: must be held to read/update control file or create * new log file. * - * CheckpointLock: must be held to do a checkpoint or restartpoint (ensures - * only one checkpointer at a time; currently, with all checkpoints done by - * the checkpointer, this is just pro forma). - * *---------- */ @@ -8864,14 +8860,6 @@ CreateCheckPoint(int flags) */ InitXLogInsert(); - /* - * Acquire CheckpointLock to ensure only one checkpoint happens at a time. - * (This is just pro forma, since in the present system structure there is - * only one process that is allowed to issue checkpoints at any given - * time.) - */ - LWLockAcquire(CheckpointLock, LW_EXCLUSIVE); - /* * Prepare to accumulate statistics. * @@ -8941,7 +8929,6 @@ CreateCheckPoint(int flags) if (last_important_lsn == ControlFile->checkPoint) { WALInsertLockRelease(); - LWLockRelease(CheckpointLock); END_CRIT_SECTION(); ereport(DEBUG1, (errmsg("checkpoint skipped because system is idle"))); @@ -9241,15 +9228,12 @@ CreateCheckPoint(int flags) CheckpointStats.ckpt_segs_added, CheckpointStats.ckpt_segs_removed, CheckpointStats.ckpt_segs_recycled); - - LWLockRelease(CheckpointLock); } /* * Mark the end of recovery in WAL though without running a full checkpoint. * We can expect that a restartpoint is likely to be in progress as we - * do this, though we are unwilling to wait for it to complete. So be - * careful to avoid taking the CheckpointLock anywhere here. + * do this, though we are unwilling to wait for it to complete. * * CreateRestartPoint() allows for the case where recovery may end before * the restartpoint completes so there is no concern of concurrent behaviour. @@ -9399,12 +9383,6 @@ CreateRestartPoint(int flags) XLogSegNo _logSegNo; TimestampTz xtime; - /* - * Acquire CheckpointLock to ensure only one restartpoint or checkpoint - * happens at a time. - */ - LWLockAcquire(CheckpointLock, LW_EXCLUSIVE); - /* Get a local copy of the last safe checkpoint record. */ SpinLockAcquire(&XLogCtl->info_lck); lastCheckPointRecPtr = XLogCtl->lastCheckPointRecPtr; @@ -9420,7 +9398,6 @@ CreateRestartPoint(int flags) { ereport(DEBUG2, (errmsg("skipping restartpoint, recovery has already ended"))); - LWLockRelease(CheckpointLock); return false; } @@ -9455,7 +9432,6 @@ CreateRestartPoint(int flags) UpdateControlFile(); LWLockRelease(ControlFileLock); } - LWLockRelease(CheckpointLock); return false; } @@ -9621,8 +9597,6 @@ CreateRestartPoint(int flags) xtime ? errdetail("Last completed transaction was at log time %s.", timestamptz_to_str(xtime)) : 0)); - LWLockRelease(CheckpointLock); - /* * Finally, execute archive_cleanup_command, if any. */ diff --git a/src/backend/replication/logical/origin.c b/src/backend/replication/logical/origin.c index 77781d059d..9bd761a426 100644 --- a/src/backend/replication/logical/origin.c +++ b/src/backend/replication/logical/origin.c @@ -559,8 +559,8 @@ CheckPointReplicationOrigin(void) tmppath))); /* - * no other backend can perform this at the same time, we're protected by - * CheckpointLock. + * no other backend can perform this at the same time; only one + * checkpoint can happen at a time. */ tmpfd = OpenTransientFile(tmppath, O_CREAT | O_EXCL | O_WRONLY | PG_BINARY); diff --git a/src/backend/storage/lmgr/lwlocknames.txt b/src/backend/storage/lmgr/lwlocknames.txt index 774292fd94..6c7cf6c295 100644 --- a/src/backend/storage/lmgr/lwlocknames.txt +++ b/src/backend/storage/lmgr/lwlocknames.txt @@ -15,7 +15,7 @@ SInvalWriteLock 6 WALBufMappingLock 7 WALWriteLock 8 ControlFileLock 9 -CheckpointLock 10 +# 10 was CheckpointLock XactSLRULock 11 SubtransSLRULock 12 MultiXactGenLock 13 -- 2.24.3 (Apple Git-128)