From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Merlin Moncure <mmoncure(at)gmail(dot)com>, Peter Geoghegan <pg(at)heroku(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: hung backends stuck in spinlock heavy endless loop |
Date: | 2015-01-14 15:17:29 |
Message-ID: | 20150114151729.GR5245@awork2.anarazel.de |
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Lists: | pgsql-hackers |
On 2015-01-14 10:13:32 -0500, Tom Lane wrote:
> Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
> > Yes, it is pg_class is coming from LockBufferForCleanup (). As you
> > can see above, it has a shorter runtime. So it was killed off once
> > about a half hour ago which did not free up the logjam. However, AV
> > spawned it again and now it does not respond to cancel.
>
> Interesting. That seems like there might be two separate issues at
> play. It's plausible that LockBufferForCleanup might be interfering
> with other attempts to scan the index, but then why wouldn't killing
> the AV have unstuck things?
LockBufferForCleanup() unfortunately isn't interruptible. I've every now
and then seen vacuums being stuck for a long while, trying to acquire
cleanup locks - IIRC I complained about that on list even. So autovac
will only be cancelled when going to the next page. And even if the
page ever gets a zero (well, one) refcount, by the time autovac is woken
up via the semaphore, it'll often end up being used again.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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