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Re: max_standby_delay considered harmful

Florian Pflug <fgp@phlo.org>

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From: Florian Pflug <fgp@phlo.org>
To: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Dimitri Fontaine <dfontaine@hi-media.com>, Tom Lane <tgl@sss.pgh.pa.us>, pgsql-hackers@postgresql.org, Bruce Momjian <bruce@momjian.us>, Greg Smith <greg@2ndquadrant.com>, Simon Riggs <simon@2ndquadrant.com>, Josh Berkus <josh@agliodbs.com>
Date: 2010-05-10T10:13:48Z
Lists: pgsql-hackers 
On May 10, 2010, at 11:43 , Heikki Linnakangas wrote:
> If you're not going to apply any more WAL records before shutdown, you
> could also just release all the AccessExclusiveLocks held by the startup
> process. Whatever the transaction was doing with the locked relation, if
> we're not going to replay any more WAL records before shutdown, we will
> not see the transaction committing or doing anything else with the
> relation, so we should be safe. Whatever state the data on disk is in,
> it must be valid, or we would have a problem with crash recovery
> recovering up to this WAL record and then starting up too.

Sounds plausible. But wouldn't this imply that HS could *always* postpone the acquisition of an AccessExclusiveLocks until right before the corresponding commit record is replayed? If fail to see a case where this would fail, yet recovery in case of an intermediate crash would be correct.

best regards,
Florian Pflug