Message-ID: <4B72E48E.7060606@enterprisedb.com>
Date: Wed, 10 Feb 2010 18:53:34 +0200
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Organization: EnterpriseDB
User-Agent: Mozilla-Thunderbird 2.0.0.22 (X11/20090706)
MIME-Version: 1.0
To: Aidan Van Dyk <aidan@highrise.ca>
CC: Fujii Masao <masao.fujii@gmail.com>,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Re: [COMMITTERS] pgsql: Make standby server	continuously
	retry  restoring the next WAL
References: <20100127152751.3B2047541B9@cvs.postgresql.org>
	<3f0b79eb1002092105r21e009d3v468496058ba04392@mail.gmail.com>
	<4B726120.80007@enterprisedb.com>
	<20100210134500.GM3670@oak.highrise.ca>
In-Reply-To: <20100210134500.GM3670@oak.highrise.ca>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

Aidan Van Dyk wrote:
> * Heikki Linnakangas <heikki.linnakangas@enterprisedb.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