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Re: Re: [COMMITTERS] pgsql: Make standby server continuously retry restoring the next WAL

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Aidan Van Dyk <aidan(at)highrise(dot)ca>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Re: [COMMITTERS] pgsql: Make standby server continuously retry restoring the next WAL
Date: 2010-02-10 16:53:34
Message-ID: 4B72E48E.7060606@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-docspgsql-hackers
Aidan Van Dyk wrote:
> * Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> [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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