Re: Hot Standby and prepared transactions

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Hiroyuki Yamada <yamada(at)kokolink(dot)net>
Cc: Simon Riggs <simon(at)2ndQuadrant(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Hot Standby and prepared transactions
Date: 2009-12-17 11:24:52
Message-ID: 4B2A1504.5030602@enterprisedb.com
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Hiroyuki Yamada wrote:
> The implementation assumes that transactions write COMMIT/ABORT WAL at the end
> of them, while it does not seem to write ABORT WAL in immediate shutdown. So,
>
> 1. acquire ACCESS EXCLUSIVE lock in table A in xact 1
> 2. execute immediate shutdown of the active node
> 3. restart it
> 4. acquire ACCESS EXCLUSIVE lock in table A in xact 2
>
> ...then, duplicate lock acquisition by two diffrent transactions can occur in the standby node.
>
> Am I missing something ? Or is this already reported ?

Replay of the shutdown checkpoint that is written when the server is
restarted should abort the old transaction and release its locks.

Hmm, looking at the code, I think Simon threw that baby with the
bathwater when he removed support for starting standby from a shutdown
checkpoint.

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com

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