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Re: postmaster 8.2 eternally hangs in sempaphore lock acquiring

From: Martin Pitt <martin(dot)pitt(at)ubuntu(dot)com>
To: pgsql-bugs(at)postgresql(dot)org
Cc: Mark Shuttleworth <mark(at)ubuntu(dot)com>
Subject: Re: postmaster 8.2 eternally hangs in sempaphore lock acquiring
Date: 2007-03-29 18:12:53
Message-ID: 20070329181253.GF13287@piware.de (view raw or flat)
Thread:
Lists: pgsql-bugs
Hi Tom, hi Mark,

Tom, thank you for having a look into this!

Tom Lane [2007-03-29 13:49 -0400]:
> Martin Pitt <martin(at)piware(dot)de> writes:
> > https://launchpad.net/bugs/93042 has symbolic gdb backtraces of all
> > three processes that are involved.
> 
> Are these really all the processes involved?  The createdb process and
> the autovac process are both waiting for someone else to give up the
> BtreeVacuumLock, but that is never held for any long period, and it's
> certainly not held by the guy trying to do InitPostgres.

There are more processes, unfortunately I don't have backtraces of
them. I got this from my IRC log:

15928 ?        Ss     0:00 postgres: mark launchpad_ftest_template [local] CREATE DATABASE
15956 ?        Ss     0:00 postgres: session session_dev [local] idle
15957 ?        Ss     0:00 postgres: launchpad launchpad_dev [local] idle
15958 ?        Ss     0:00 postgres: session session_dev [local] idle
15969 ?        Ss     0:00 postgres: launchpad launchpad_dev [local] idle
16014 ?        Ss     0:00 postgres: launchpad launchpad_dev [local] idle
16273 ?        Ss     0:00 postgres: mark launchpad_ftest_template [local] startup waiting

> I believe that the guy trying to do InitPostgres is blocked by the
> createdb process --- it looks like he's trying to attach to the same 
> DB being used as a template for the createdb, and as of 8.2 we lock out
> new entries to a template DB until the copy is complete.
> 
> It's possible that this is not a deadlock per se, but the aftermath of
> someone having errored out without releasing the BtreeVacuumLock --- but
> I don't entirely see how that could happen either, at least not without
> a core dump scenario.
> 
> Is there anything in the postmaster log when this happens?  Errors out
> of _bt_start_vacuum would be particularly interesting...

I believe Mark's postgres runs with fully verbose logging. Mark, can you please
have a look?

Thanks,

Martin
-- 
Martin Pitt        http://www.piware.de
Ubuntu Developer   http://www.ubuntu.com
Debian Developer   http://www.debian.org

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Next:From: Mark ShuttleworthDate: 2007-03-29 18:20:58
Subject: Re: postmaster 8.2 eternally hangs in sempaphore lock acquiring
Previous:From: Tom LaneDate: 2007-03-29 17:49:23
Subject: Re: postmaster 8.2 eternally hangs in sempaphore lock acquiring

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