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Add logging for excessive ProcSignalBarrier waits.

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To enable diagnosis of systems that are not processing ProcSignalBarrier
requests promptly, add a LOG message every 5 seconds if we seem to be
wedged.  Although you could already see this state as a wait event in
pg_stat_activity, the log message also shows the PID of the process that
is preventing progress.

Also add DEBUG1 logging around the whole wait loop.

Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Discussion: https://postgr.es/m/CA%2BTgmoYJ03r5359gQutRGP9BtigYCg3_UskcmnVjBf-QO3-0pQ%40mail.gmail.com
This commit is contained in:
Thomas Munro 2022-05-11 18:03:03 +12:00
parent f95d53eded
commit 0d3431497d
1 changed files with 16 additions and 2 deletions
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18
src/backend/storage/ipc/procsignal.c
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@ -393,6 +393,11 @@ WaitForProcSignalBarrier(uint64 generation)
{
Assert(generation <= pg_atomic_read_u64(&ProcSignal->psh_barrierGeneration));
elog(DEBUG1,
"waiting for all backends to process ProcSignalBarrier generation "
UINT64_FORMAT,
generation);
for (int i = NumProcSignalSlots - 1; i >= 0; i--)
{
ProcSignalSlot *slot = &ProcSignal->psh_slot[i];
@ -407,13 +412,22 @@ WaitForProcSignalBarrier(uint64 generation)
oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
while (oldval < generation)
{
ConditionVariableSleep(&slot->pss_barrierCV,
WAIT_EVENT_PROC_SIGNAL_BARRIER);
if (ConditionVariableTimedSleep(&slot->pss_barrierCV,
5000,
WAIT_EVENT_PROC_SIGNAL_BARRIER))
ereport(LOG,
(errmsg("still waiting for backend with PID %lu to accept ProcSignalBarrier",
(unsigned long) slot->pss_pid)));
oldval = pg_atomic_read_u64(&slot->pss_barrierGeneration);
}
ConditionVariableCancelSleep();
}
elog(DEBUG1,
"finished waiting for all backends to process ProcSignalBarrier generation "
UINT64_FORMAT,
generation);
/*
* The caller is probably calling this function because it wants to read
* the shared state or perform further writes to shared state once all