Re: Parallel Seq Scan

On Tue, Mar 17, 2015 at 1:42 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> The problem occurs in second loop inside DestroyParallelContext()
> where it calls WaitForBackgroundWorkerShutdown(). Basically
> WaitForBackgroundWorkerShutdown() just checks for BGWH_STOPPED
> status, refer below code in parallel-mode patch:
>
> + status = GetBackgroundWorkerPid(handle, &pid);
> + if (status == BGWH_STOPPED)
> + return status;
>
> So if the status here returned is BGWH_NOT_YET_STARTED, then it
> will go for WaitLatch and will there forever.
>
> I think fix is to check if status is BGWH_STOPPED or BGWH_NOT_YET_STARTED,
> then just return the status.
>
> What do you say?

No, that's not right. If we return when the status is
BGWH_NOT_YET_STARTED, then the postmaster could subsequently start the
worker.

Can you try this:

diff --git a/src/backend/postmaster/bgworker.c
b/src/backend/postmaster/bgworker.c
index f80141a..39b919f 100644
--- a/src/backend/postmaster/bgworker.c
+++ b/src/backend/postmaster/bgworker.c
@@ -244,6 +244,8 @@ BackgroundWorkerStateChange(void)
rw->rw_terminate = true;
if (rw->rw_pid != 0)
kill(rw->rw_pid, SIGTERM);
+ else
+ ReportBackgroundWorkerPID(rw);
}
continue;
}

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company