Why does xlog.c not treat COMMIT_PREPARED/ABORT_PREPARED as commit/abort?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: pgsql-hackers(at)postgreSQL(dot)org
Subject: Why does xlog.c not treat COMMIT_PREPARED/ABORT_PREPARED as commit/abort?
Date: 2014-07-24 21:53:17
Message-ID: 20552.1406238797@sss.pgh.pa.us
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There's a bunch of code in xlog.c that special-cases commit/abort records
for purposes of controlling replay, ie whether you can pause before/after
a particular xlog record, extract a timestamp from it, etc. This code
does not, and apparently never has, counted COMMIT_PREPARED or
ABORT_PREPARED as commit/abort records. Is there a good reason for that,
or is it just an oversight?

I noticed this in investigation of bug #11032, which is a side effect
of the fact that xlog.c doesn't believe there's any timestamp to be
found in COMMIT_PREPARED records. But more generally, they can't be
used as recovery targets, and I don't see a reason for that.

Assuming we agree that this is a bug, is it something to back-patch,
or do we not want to change back-branch behavior here?

regards, tom lane

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