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Re: Deleted WAL files held open by backends in Linux

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: Deleted WAL files held open by backends in Linux
Date: 2009-12-01 15:12:46
Message-ID: 964.1259680366@sss.pgh.pa.us (view raw or flat)
Thread:
Lists: pgsql-hackers
"Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> Is there a reasonably cheap way to check whether the backend has a
> WAL file open and whether that one is the current append target?

Detecting whether we have a WAL file open is trivial (just look at
the static variable holding the file descriptor).  Determining whether
it's still the current append target is not so cheap though; it would
require examining shared-memory status which means taking a lock on
that status (and it's a high-traffic lock already).

We could have the open WAL file dropped if stale as a side-effect
anytime we have occasion to examine that shared state anyway.  But
in a nearly-read-only session such as your example I'm not sure that
would happen often enough to fix the problem.

			regards, tom lane

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