Improve tests for postmaster death in auxiliary processes.

In checkpointer and walwriter, avoid calling PostmasterIsAlive unless
WaitLatch has reported WL_POSTMASTER_DEATH.  This saves a kernel call per
iteration of the process's outer loop, which is not all that much, but a
cycle shaved is a cycle earned.  I had already removed the unconditional
PostmasterIsAlive calls in bgwriter and pgstat in previous patches, but
forgot that WL_POSTMASTER_DEATH is supposed to be treated as untrustworthy
(per comment in unix_latch.c); so adjust those two cases to match.

There are a few other places where the same idea might be applied, but only
after substantial code rearrangement, so I didn't bother.

1 files changed, 13 insertions, 10 deletions

diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index fa3435710d7..7f8ba95c44d 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -374,18 +374,12 @@ CheckpointerMain(void)
 		pg_time_t	now;
 		int			elapsed_secs;
 		int			cur_timeout;
+		int			rc;
 
 		/* Clear any already-pending wakeups */
 		ResetLatch(&MyProc->procLatch);
 
 		/*
-		 * Emergency bailout if postmaster has died.  This is to avoid the
-		 * necessity for manual cleanup of all postmaster children.
-		 */
-		if (!PostmasterIsAlive())
-			exit(1);
-
-		/*
 		 * Process any requests or signals received recently.
 		 */
 		AbsorbFsyncRequests();
@@ -581,9 +575,18 @@ CheckpointerMain(void)
 			cur_timeout = Min(cur_timeout, XLogArchiveTimeout - elapsed_secs);
 		}
 
-		(void) WaitLatch(&MyProc->procLatch,
-						 WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
-						 cur_timeout * 1000L /* convert to ms */);
+		rc = WaitLatch(&MyProc->procLatch,
+					   WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+					   cur_timeout * 1000L /* convert to ms */);
+
+		/*
+		 * Emergency bailout if postmaster has died.  This is to avoid the
+		 * necessity for manual cleanup of all postmaster children.  Note
+		 * that we mustn't trust the WL_POSTMASTER_DEATH result flag entirely;
+		 * if it is set, recheck with PostmasterIsAlive before believing it.
+		 */
+		if ((rc & WL_POSTMASTER_DEATH) && !PostmasterIsAlive())
+			exit(1);
 	}
 }