Re: hung backends stuck in spinlock heavy endless loop

From: Peter Geoghegan <pg(at)heroku(dot)com>
To: Andres Freund <andres(at)2ndquadrant(dot)com>
Cc: Merlin Moncure <mmoncure(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: hung backends stuck in spinlock heavy endless loop
Date: 2015-01-13 23:49:33
Message-ID: CAM3SWZQmAWR0Z6MgQMYzAGgzRGC498CCnJih18bj7Ydat4c93A@mail.gmail.com
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On Tue, Jan 13, 2015 at 3:21 PM, Andres Freund <andres(at)2ndquadrant(dot)com> wrote:
> My guess is rather that it's contention on the freelist lock via
> StrategyGetBuffer's. I've seen profiles like this due to exactly that
> before - and it fits to parallel loading quite well.

I'm not saying you're wrong, but the breakdown of _bt_moveright()
relative to _bt_relandgetbuf() calls seems a bit fishy to me.

I don't remember seeing _bt_moveright() or _bt_compare() figuring so
prominently, where _bt_binsrch() is nowhere to be seen. I can't see a
reference to _bt_binsrch() in either profile.

--
Peter Geoghegan

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