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Reduce more the number of calls to GetMaxBackends() 

Some of the code paths changed by aa64f23 can reduce the number of times
GetMaxBackends() is called.  The performance gain is marginal, but most
of the code changed by this commit already did that.  Hence, let's be
clean and apply the same rule everywhere, for consistency.

Some of the code paths, like in deadlock.c, involve only assertions.
These are left unchanged.

Reviewed-by: Nathan Bossart, Robert Haas
Discussion: https://postgr.es/m/YgMpGZhPOjNfS7er@paquier.xyz
This commit is contained in:
Michael Paquier 2022-02-10 10:27:29 +09:00
parent f0cd9097cf
commit 4567596316
3 changed files with 10 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
src/backend/commands/async.c
View File

@ -1633,6 +1633,7 @@ SignalBackends(void)
int32 *pids;
BackendId *ids;
int count;
int max_backends = GetMaxBackends();
/*
* Identify backends that we need to signal. We don't want to send
@ -1642,8 +1643,8 @@ SignalBackends(void)
* XXX in principle these pallocs could fail, which would be bad. Maybe
* preallocate the arrays? They're not that large, though.
*/
pids = (int32 *) palloc(GetMaxBackends() * sizeof(int32));
ids = (BackendId *) palloc(GetMaxBackends() * sizeof(BackendId));
pids = (int32 *) palloc(max_backends * sizeof(int32));
ids = (BackendId *) palloc(max_backends * sizeof(BackendId));
count = 0;
LWLockAcquire(NotifyQueueLock, LW_EXCLUSIVE);

7
src/backend/storage/lmgr/lock.c
View File

@ -2924,6 +2924,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
LWLock *partitionLock;
int count = 0;
int fast_count = 0;
int max_backends = GetMaxBackends();
if (lockmethodid <= 0 || lockmethodid >= lengthof(LockMethods))
elog(ERROR, "unrecognized lock method: %d", lockmethodid);
@ -2942,12 +2943,12 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
vxids = (VirtualTransactionId *)
MemoryContextAlloc(TopMemoryContext,
sizeof(VirtualTransactionId) *
(GetMaxBackends() + max_prepared_xacts + 1));
(max_backends + max_prepared_xacts + 1));
}
else
vxids = (VirtualTransactionId *)
palloc0(sizeof(VirtualTransactionId) *
(GetMaxBackends() + max_prepared_xacts + 1));
(max_backends + max_prepared_xacts + 1));
/* Compute hash code and partition lock, and look up conflicting modes. */
hashcode = LockTagHashCode(locktag);
@ -3104,7 +3105,7 @@ GetLockConflicts(const LOCKTAG *locktag, LOCKMODE lockmode, int *countp)
LWLockRelease(partitionLock);
if (count > GetMaxBackends() + max_prepared_xacts) /* should never happen */
if (count > max_backends + max_prepared_xacts) /* should never happen */
elog(PANIC, "too many conflicting locks found");
vxids[count].backendId = InvalidBackendId;

5
src/backend/utils/adt/lockfuncs.c
View File

@ -559,13 +559,14 @@ pg_safe_snapshot_blocking_pids(PG_FUNCTION_ARGS)
int *blockers;
int num_blockers;
Datum *blocker_datums;
int max_backends = GetMaxBackends();
/* A buffer big enough for any possible blocker list without truncation */
blockers = (int *) palloc(GetMaxBackends() * sizeof(int));
blockers = (int *) palloc(max_backends * sizeof(int));
/* Collect a snapshot of processes waited for by GetSafeSnapshot */
num_blockers =
GetSafeSnapshotBlockingPids(blocked_pid, blockers, GetMaxBackends());
GetSafeSnapshotBlockingPids(blocked_pid, blockers, max_backends);
/* Convert int array to Datum array */
if (num_blockers > 0)