Avoid calling kill() in a postmaster signal handler.

This causes problems when the system load is high, per report from Zdenek
Kotala in <1250860954.1239.114.camel@localhost>; instead of calling kill
directly, have the signal handler set a flag which is checked in ServerLoop.
This way, the handler can return before being called again by a subsequent
signal sent from the autovacuum launcher.  Also, increase the sleep in the
launcher in this failure path to 1 second.

Backpatch to 8.3, which is when the signalling between autovacuum
launcher/postmaster was introduced.

Also, add a couple of ReleasePostmasterChildSlot calls in error paths; this
part backpatched to 8.4 which is when the child slot stuff was introduced.

diff --git a/src/backend/postmaster/autovacuum.c b/src/backend/postmaster/autovacuum.c
index 2e97f6726eed31e9c29ac3e6bf147597bccfcfac..858ce70d601ffa91de066790a44113d455207457 100644 (file)
--- a/src/backend/postmaster/autovacuum.c
+++ b/src/backend/postmaster/autovacuum.c
@@ -653,7 +653,7 @@ AutoVacLauncherMain(int argc, char *argv[])
                                 * of a worker will continue to fail in the same way.
                                 */
                                AutoVacuumShmem->av_signal[AutoVacForkFailed] = false;
-                               pg_usleep(100000L);             /* 100ms */
+                               pg_usleep(1000000L);            /* 1s */
                                SendPostmasterSignal(PMSIGNAL_START_AUTOVAC_WORKER);
                                continue;
                        }

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index fad472e8895c43b28ed268c330cca455fd1f9ae9..ff947a3b6fdf5db1f4833735ca9b294ac05cd8f9 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -290,6 +290,8 @@ bool                redirection_done = false;       /* stderr redirected for syslogger? */
 
 /* received START_AUTOVAC_LAUNCHER signal */
 static volatile sig_atomic_t start_autovac_launcher = false;
+/* the launcher needs to be signalled to communicate some condition */
+static volatile bool           avlauncher_needs_signal = false;
 
 /*
  * State for assigning random salts and cancel keys.
@@ -1391,6 +1393,14 @@ ServerLoop(void)
                if (PgStatPID == 0 && pmState == PM_RUN)
                        PgStatPID = pgstat_start();
 
+               /* If we need to signal the autovacuum launcher, do so now */
+               if (avlauncher_needs_signal)
+               {
+                       avlauncher_needs_signal = false;
+                       if (AutoVacPID != 0)
+                               kill(AutoVacPID, SIGUSR1);
+               }
+
                /*
                 * Touch the socket and lock file every 58 minutes, to ensure that
                 * they are not removed by overzealous /tmp-cleaning tasks.  We assume
@@ -3014,6 +3024,7 @@ BackendStartup(Port *port)
                /* in parent, fork failed */
                int                     save_errno = errno;
 
+               (void) ReleasePostmasterChildSlot(bn->child_slot);
                free(bn);
                errno = save_errno;
                ereport(LOG,
@@ -4343,6 +4354,7 @@ StartAutovacuumWorker(void)
                         * fork failed, fall through to report -- actual error message was
                         * logged by StartAutoVacWorker
                         */
+                       (void) ReleasePostmasterChildSlot(bn->child_slot);
                        free(bn);
                }
                else
@@ -4354,12 +4366,16 @@ StartAutovacuumWorker(void)
        /*
         * Report the failure to the launcher, if it's running.  (If it's not, we
         * might not even be connected to shared memory, so don't try to call
-        * AutoVacWorkerFailed.)
+        * AutoVacWorkerFailed.)  Note that we also need to signal it so that it
+        * responds to the condition, but we don't do that here, instead waiting
+        * for ServerLoop to do it.  This way we avoid a ping-pong signalling in
+        * quick succession between the autovac launcher and postmaster in case
+        * things get ugly.
         */
        if (AutoVacPID != 0)
        {
                AutoVacWorkerFailed();
-               kill(AutoVacPID, SIGUSR1);
+               avlauncher_needs_signal = true;
        }
 }