Make pg_promote() detect postmaster death while waiting for promotion to end.

Previously even if postmaster died and WaitLatch() woke up with that event
while pg_promote() was waiting for the standby promotion to finish,
pg_promote() did nothing special and kept waiting until timeout occurred.
This could cause a busy loop.

This patch make pg_promote() return false immediately when postmaster
dies, to avoid such a busy loop.

Back-patch to v12 where pg_promote() was added.

Author: Fujii Masao
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/CAHGQGwEs9ROgSp+QF+YdDU+xP8W=CY1k-_Ov-d_Z3JY+to3eXA@mail.gmail.com

diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index 4795c6fa947a8a379516e8fe8a4cc8aecd975dd3..8a70503228dd8a3808f0fe275ee508ac13219109 100644 (file)
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -759,6 +759,8 @@ pg_promote(PG_FUNCTION_ARGS)
 #define WAITS_PER_SECOND 10
    for (i = 0; i < WAITS_PER_SECOND * wait_seconds; i++)
    {
+       int         rc;
+
        ResetLatch(MyLatch);
 
        if (!RecoveryInProgress())
@@ -766,10 +768,17 @@ pg_promote(PG_FUNCTION_ARGS)
 
        CHECK_FOR_INTERRUPTS();
 
-       (void) WaitLatch(MyLatch,
-                        WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
-                        1000L / WAITS_PER_SECOND,
-                        WAIT_EVENT_PROMOTE);
+       rc = WaitLatch(MyLatch,
+                      WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+                      1000L / WAITS_PER_SECOND,
+                      WAIT_EVENT_PROMOTE);
+
+       /*
+        * Emergency bailout if postmaster has died.  This is to avoid the
+        * necessity for manual cleanup of all postmaster children.
+        */
+       if (rc & WL_POSTMASTER_DEATH)
+           PG_RETURN_BOOL(false);
    }
 
    ereport(WARNING,