Centralize logic for skipping useless ereport/elog calls.

While ereport() and elog() themselves are quite cheap when the
error message level is too low to be printed, some places need to do
substantial work before they can call those macros at all.  To allow
optimizing away such setup work when nothing is to be printed, make
elog.c export a new function message_level_is_interesting(elevel)
that reports whether ereport/elog will do anything.  Make use of that
in various places that had ad-hoc direct tests of log_min_messages etc.
Also teach ProcSleep to use it to avoid some work.  (There may well
be other places that could usefully use this; I didn't search hard.)

Within elog.c, refactor a little bit to avoid having duplicate copies
of the policy-setting logic.  When that code was written, we weren't
relying on the availability of inline functions; so it had some
duplications in the name of efficiency, which I got rid of.

Alvaro Herrera and Tom Lane

Discussion: https://postgr.es/m/129515.1606166429@sss.pgh.pa.us

1 files changed, 22 insertions, 18 deletions

diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c
index 40eac704dc0..7dc3911590e 100644
--- a/src/backend/storage/lmgr/proc.c
+++ b/src/backend/storage/lmgr/proc.c
@@ -1337,26 +1337,30 @@ ProcSleep(LOCALLOCK *locallock, LockMethod lockMethodTable)
 				!(statusFlags & PROC_VACUUM_FOR_WRAPAROUND))
 			{
 				int			pid = autovac->pid;
-				StringInfoData locktagbuf;
-				StringInfoData logbuf;	/* errdetail for server log */
 
 				/* report the case, if configured to do so */
-				initStringInfo(&locktagbuf);
-				initStringInfo(&logbuf);
-				DescribeLockTag(&locktagbuf, &locktag_copy);
-				appendStringInfo(&logbuf,
-								 _("Process %d waits for %s on %s."),
-								 MyProcPid,
-								 GetLockmodeName(lockmethod_copy, lockmode),
-								 locktagbuf.data);
-
-				ereport(DEBUG1,
-						(errmsg("sending cancel to blocking autovacuum PID %d",
-								pid),
-						 errdetail_log("%s", logbuf.data)));
-
-				pfree(logbuf.data);
-				pfree(locktagbuf.data);
+				if (message_level_is_interesting(DEBUG1))
+				{
+					StringInfoData locktagbuf;
+					StringInfoData logbuf;	/* errdetail for server log */
+
+					initStringInfo(&locktagbuf);
+					initStringInfo(&logbuf);
+					DescribeLockTag(&locktagbuf, &locktag_copy);
+					appendStringInfo(&logbuf,
+									 _("Process %d waits for %s on %s."),
+									 MyProcPid,
+									 GetLockmodeName(lockmethod_copy, lockmode),
+									 locktagbuf.data);
+
+					ereport(DEBUG1,
+							(errmsg("sending cancel to blocking autovacuum PID %d",
+									pid),
+							 errdetail_log("%s", logbuf.data)));
+
+					pfree(locktagbuf.data);
+					pfree(logbuf.data);
+				}
 
 				/* send the autovacuum worker Back to Old Kent Road */
 				if (kill(pid, SIGINT) < 0)