Re: Deleted WAL files held open by backends in Linux

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Deleted WAL files held open by backends in Linux
Date: 2009-11-30 21:24:53
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Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> There has to be something causing those sessions to touch WAL, and
> the dirty-buffer scenario doesn't seem reliable enough.

This is seeming fairly likely to be the cause, though. It may be a
combination of the nightly VACUUM FREEZE ANALYZE we typically do on
every database and the monitoring software, which would directly run
a couple queries each five seconds or so, and would also exercise
the software publishers on a similar schedule. My "smoking gun" is
that the monitoring software was restarted last night after the time
that the nightly vacuums would have completed, and its connections
are not showing as having a deleted WAL file open today.

I was unable to directly cause the a backend to open a WAL file by
connecting through JDBC and running the same kind of queries used by
the software publisher, which does tend to point to some indirect
mechanism, like the dirty buffer flushing.


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