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From: Heikki Linnakangas <[email protected]>
To: Aidan Van Dyk <[email protected]>
Cc: Fujii Masao <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Subject: Re: Re: [COMMITTERS] pgsql: Make standby server	continuously retry  restoring the next WAL
Date: Wed, 10 Feb 2010 18:53:34 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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Aidan Van Dyk wrote:
> * Heikki Linnakangas <[email protected]> [100210 02:33]:
>  
>> Hmm, so after running restore_command, check the file size and if it's
>> too short, treat it the same as if restore_command returned non-zero?
>> And it will be retried on the next iteration. Works for me, though OTOH
>> it will then fail to complain about a genuinely WAL file that's
>> truncated for some reason. I guess there's no way around that, even if
>> you have a script as restore_command that does the file size check, it
>> will have the same problem.
> 
> But isn't this something every current PITR archive already "works
> around"...  Everybody doing PITR archives already know the importance of
> making the *appearance* of the WAL filename in the archive atomic.

Well, pg_standby does defend against that, but you don't use pg_standby
with the built-in standby mode anymore. It would be reasonable to have
the same level of defenses built-in. It's essentially a one-line change,
and saves a lot of trouble and risk of subtle misconfiguration for admins.

> Don't docs warn about plain cp not being atomic and allowing "short"
> files to appear in the archive... 

Hmm, I don't see anything about that at quick glance. Besides, normal
PITR doesn't have a problem with that, because it will stop when it
reaches the end of archived WAL anyway.

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

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