From: Jim Vanns <james.vanns@framestore.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jim Vanns <james.vanns@framestore.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Odd blocking (or massively latent) issue - even with EXPLAIN
Date: Mon, 23 Jul 2012 16:49:25 +0100
Message-ID: <1343058565.12579.126.camel@sys367.ldn.framestore.com> (raw)
In-Reply-To: <29948.1343056156@sss.pgh.pa.us>
References: <1343032905.12579.3.camel@sys367.ldn.framestore.com>
<29948.1343056156@sss.pgh.pa.us>
On Mon, 2012-07-23 at 11:09 -0400, Tom Lane wrote:
> Jim Vanns <james.vanns@framestore.com> writes:
> > We're seeing SELECT statements and even EXPLAIN (no ANAYLZE)
> > statements hang indefinitely until *something* (we don't know what)
> > releases some kind of resource or no longer becomes a massive bottle
> > neck. These are the symptoms.
>
> Does anything show up as blocked in the pg_locks view?
Nope.
> Could you attach to the stuck process with gdb and get a stack trace?
Haven't been quite brave enough to do that yet - this is a production
server. I did manage to strace a process though - it (the server side
process of a psql EXPLAIN) appeared to spin on an awful lot of semop()
calls with the occasional read(). Of course, in the context of a shared
memory system such as postgres I'd expect to see quite a lot of semop()
calls but I've no idea how much is normal and how much is excessive.
Jim
> regards, tom lane
>
--
Jim Vanns
Systems Programmer
Framestore
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To: pgsql-performance@postgresql.org
Cc: james.vanns@framestore.com, tgl@sss.pgh.pa.us
Subject: Re: Odd blocking (or massively latent) issue - even with EXPLAIN
In-Reply-To: <1343058565.12579.126.camel@sys367.ldn.framestore.com>
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