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Commitaea5d29

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committed
Notify bgworker registrant after freeing worker slot.
Tom Lane observed buildfarm failures caused by the select_parallelregression test trying to launch new parallel queries before theworker slots used by the previous ones were freed. Try to fix this byhaving the postmaster free the worker slots before it sends theSIGUSR1 notifications to the registering process. This doesn'tcompletely eliminate the possibility that the user backend might(correctly) observe the worker as dead before the slot is free, but Ibelieve 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
1 parent5a73e17 commitaea5d29

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3 files changed

+37
-3
lines changed

3 files changed

+37
-3
lines changed

‎src/backend/postmaster/bgworker.c

Lines changed: 33 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -429,6 +429,39 @@ ReportBackgroundWorkerPID(RegisteredBgWorker *rw)
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kill(rw->rw_worker.bgw_notify_pid,SIGUSR1);
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}
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/*
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* Report that the PID of a background worker is now zero because a
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* previously-running background worker has exited.
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*
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* This function should only be called from the postmaster.
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*/
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void
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ReportBackgroundWorkerExit(slist_mutable_iter*cur)
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{
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RegisteredBgWorker*rw;
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BackgroundWorkerSlot*slot;
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rw=slist_container(RegisteredBgWorker,rw_lnode,cur->cur);
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Assert(rw->rw_shmem_slot<max_worker_processes);
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slot=&BackgroundWorkerData->slot[rw->rw_shmem_slot];
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slot->pid=rw->rw_pid;
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/*
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* If this worker is slated for deregistration, do that before notifying
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* the process which started it. Otherwise, if that process tries to
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* reuse the slot immediately, it might not be available yet. In theory
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* that could happen anyway if the process checks slot->pid at just the
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* wrong moment, but this makes the window narrower.
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*/
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if (rw->rw_terminate||
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rw->rw_worker.bgw_restart_time==BGW_NEVER_RESTART)
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ForgetBackgroundWorker(cur);
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if (rw->rw_worker.bgw_notify_pid!=0)
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kill(rw->rw_worker.bgw_notify_pid,SIGUSR1);
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}
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/*
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* Cancel SIGUSR1 notifications for a PID belonging to an exiting backend.
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*

‎src/backend/postmaster/postmaster.c

Lines changed: 3 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -3050,9 +3050,9 @@ CleanupBackgroundWorker(int pid,
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intexitstatus)/* child's exit status */
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{
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charnamebuf[MAXPGPATH];
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slist_iteriter;
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slist_mutable_iteriter;
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3055-
slist_foreach(iter,&BackgroundWorkerList)
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slist_foreach_modify(iter,&BackgroundWorkerList)
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{
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RegisteredBgWorker*rw;
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@@ -3126,7 +3126,7 @@ CleanupBackgroundWorker(int pid,
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rw->rw_backend=NULL;
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rw->rw_pid=0;
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rw->rw_child_slot=0;
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ReportBackgroundWorkerPID(rw);/* report child death */
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ReportBackgroundWorkerExit(&iter);/* report child death */
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LogChildExit(EXIT_STATUS_0(exitstatus) ?DEBUG1 :LOG,
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namebuf,pid,exitstatus);

‎src/include/postmaster/bgworker_internals.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -42,6 +42,7 @@ extern void BackgroundWorkerShmemInit(void);
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externvoidBackgroundWorkerStateChange(void);
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externvoidForgetBackgroundWorker(slist_mutable_iter*cur);
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externvoidReportBackgroundWorkerPID(RegisteredBgWorker*);
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externvoidReportBackgroundWorkerExit(slist_mutable_iter*cur);
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externvoidBackgroundWorkerStopNotifications(pid_tpid);
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externvoidResetBackgroundWorkerCrashTimes(void);
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