From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bruce Momjian <pgman@candle.pha.pa.us>
Cc: Richard Huxton <dev@archonet.com>
Cc: pgsql-docs@postgresql.org
Subject: Re: Proposed doc-patch: Identifying the Current WAL file
Date: Fri, 14 Apr 2006 12:07:15 -0400
Message-ID: <9932.1145030835@sss.pgh.pa.us> (raw)
In-Reply-To: <200604141544.k3EFiuw20847@candle.pha.pa.us>
References: <200604141544.k3EFiuw20847@candle.pha.pa.us>
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> Richard Huxton wrote:
>> To identify the current, partially-filled WAL segment, sort first by
>> mtime and second by file name. That is, take the latest mtime among the
>> properly-named files, breaking ties by taking the higher filename.
> I am confused by this. Why do both mtime and file name need to be
> checked?
Because recycled WAL segments are renamed to have higher file names than
the currently-in-use segment. So you can't depend on file name first.
However, shortly after a segment switch two WAL segments could have the
same mtime (to within whatever the mtime granularity is, typ. 1 second).
The proposed rule should be OK as long as checkpoints (and ensuing
renames) can't occur oftener than the mtime granularity. If you're
checkpointing more than once a second, well, you need help ...
regards, tom lane
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To: pgsql-docs@postgresql.org
Cc: tgl@sss.pgh.pa.us, pgman@candle.pha.pa.us, dev@archonet.com
Subject: Re: Proposed doc-patch: Identifying the Current WAL file
In-Reply-To: <9932.1145030835@sss.pgh.pa.us>
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