From: Tom Lane <tgl@sss.pgh.pa.us>
To: Drazen Kacar <drazen.kacar@oradian.com>
cc: pgsql-admin@postgresql.org
Subject: Re: Zeroed out pages at the end of the database files
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Comments: In-reply-to Drazen Kacar <drazen.kacar@oradian.com>
 message dated "Wed, 30 Oct 2013 17:35:23 +0100"
Date: Wed, 30 Oct 2013 12:48:40 -0400
Message-ID: <4981.1383151720@sss.pgh.pa.us>
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Drazen Kacar <drazen.kacar@oradian.com> writes:
> It turned out that pg_filedump reported errors for 34 database files, but
> that was because all those files had one or more database pages (8k) at the
> end of the file zeroed out.

This can definitely happen after a database crash; it's not a problem
since the wasted space will be recovered by VACUUM.

I don't recall at the moment if there are any code paths that can cause
it without a crash.  However, if you're looking directly at the disk
files it's definitely possible for there to be zeroes in a page that
has been obtained from the OS but never yet flushed out of shared
buffers.

			regards, tom lane


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