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Notify bgworker registrant after freeing worker slot.

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Tom Lane observed buildfarm failures caused by the select_parallel
regression test trying to launch new parallel queries before the
worker slots used by the previous ones were freed.  Try to fix this by
having the postmaster free the worker slots before it sends the
SIGUSR1 notifications to the registering process.  This doesn't
completely eliminate the possibility that the user backend might
(correctly) observe the worker as dead before the slot is free, but I
believe it should make the window significantly narrower.

Patch by me, per complaint from Tom Lane.  Reviewed by Amit Kapila.

Discussion: http://postgr.es/m/30673.1487310734@sss.pgh.pa.us
This commit is contained in:
Robert Haas
2017-03-03 09:14:49 +05:30
parent 5a73e17317
commit aea5d29836
3 changed files with 37 additions and 3 deletions
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6
src/backend/postmaster/postmaster.c
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@@ -3050,9 +3050,9 @@ CleanupBackgroundWorker(int pid,
int exitstatus) /* child's exit status */
{
char namebuf[MAXPGPATH];
slist_iter iter;
slist_mutable_iter iter;
slist_foreach(iter, &BackgroundWorkerList)
slist_foreach_modify(iter, &BackgroundWorkerList)
{
RegisteredBgWorker *rw;
@@ -3126,7 +3126,7 @@ CleanupBackgroundWorker(int pid,
rw->rw_backend = NULL;
rw->rw_pid = 0;
rw->rw_child_slot = 0;
ReportBackgroundWorkerPID(rw); /* report child death */
ReportBackgroundWorkerExit(&iter); /* report child death */
LogChildExit(EXIT_STATUS_0(exitstatus) ? DEBUG1 : LOG,
namebuf, pid, exitstatus);