From: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> |
---|---|
To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
Cc: | Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Andres Freund <andres(at)2ndquadrant(dot)com>, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Fabrízio Mello <fabriziomello(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Parallel Seq Scan |
Date: | 2015-03-19 03:43:38 |
Message-ID: | CAA4eK1LTt9VoBfNQxs-yrQ6ABcv4WOtZ6qP71dpE3cX2rAxY-w@mail.gmail.com |
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Lists: | pgsql-hackers |
On Wed, Mar 18, 2015 at 9:14 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Wed, Mar 18, 2015 at 2:22 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> >
> > It didn't fix the problem. IIUC, you have done this to ensure that
> > if worker is not already started, then update it's pid, so that we
> > can get the required status in WaitForBackgroundWorkerShutdown().
> > As this is a timing issue, it can so happen that before Postmaster
> > gets a chance to report the pid, backend has already started waiting
> > on WaitLatch().
>
> I think I figured out the problem. That fix only helps in the case
> where the postmaster noticed the new registration previously but
> didn't start the worker, and then later notices the termination.
> What's much more likely to happen is that the worker is started and
> terminated so quickly that both happen before we create a
> RegisteredBgWorker for it. The attached patch fixes that case, too.
>
Patch fixes the problem and now for Rescan, we don't need to Wait
for workers to finish.
> Assuming this actually fixes the problem, I think we should back-patch
> it into 9.4.
+1
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com
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