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Standbys, txid_current_snapshot, wraparound

From: Daniel Farina <daniel(at)heroku(dot)com>
To: pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Standbys, txid_current_snapshot, wraparound
Date: 2012-03-23 00:26:10
Message-ID: CAAZKuFbB7UR3NXV1pkZFRXy=6V1QBq_OeHJWJNTLpKBpH=QFgg@mail.gmail.com (view raw or flat)
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Some time ago I reported bug 6291[0], which reported a Xid wraparound,
both as reported in pg_controldata and by txid_current_snapshot.
Unfortunately, nobody could reproduce it.

Today, the same system of ours just passed the wraparound mark
successfully at this time, incrementing the epoch.  However, two
standbys have not done the same: they have wrapped to a low txid.  At
this time, pg_controldata does report the correct epoch, as I read it,
unlike the original case.

I have not yet tried to reproduce this in a minimal way, but I wanted
to relate this information as soon as possible.

These systems are 9.0.6, on Ubuntu 10.04 LTS, amd64.

[0]: http://archives.postgresql.org/pgsql-bugs/2011-11/msg00094.php

-- 
fdr

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