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Re: pg_streamrecv for 9.1?

From: Magnus Hagander <magnus(at)hagander(dot)net>
To: Aidan Van Dyk <aidan(at)highrise(dot)ca>
Cc: Gurjeet Singh <singh(dot)gurjeet(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, David Fetter <david(at)fetter(dot)org>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: pg_streamrecv for 9.1?
Date: 2010-12-30 12:39:19
Message-ID: AANLkTin9OFuLLkfrGk5i0RXmUp9Bf0jL+kV1O3DWuVQm@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Thu, Dec 30, 2010 at 13:30, Aidan Van Dyk <aidan(at)highrise(dot)ca> wrote:
> On Thu, Dec 30, 2010 at 6:41 AM, Magnus Hagander <magnus(at)hagander(dot)net> wrote:
>
>>> As the README says that is not self-contained (for no fault of its own) and
>>> one should typically set archive_command to guarantee zero WAL loss.
>>
>> Yes. Though you can combine it fine with wal_keep_segments if you
>> think that's safe - but archive_command is push and this tool is pull,
>> so if your backup server goes down for a while, pg_streamrecv will get
>> a gap and fail. Whereas if you configure an archive_command, it will
>> queue up the log on the master if it stops working, up to the point of
>> shutting it down because of out-of-disk. Which you *want*, if you want
>> to be really sure about the backups.
>
> I was thinking I'ld like use pg_streamrecv to "make" my archive, and
> the archive script on the master would just "verify" the archive has
> that complete segment.
>
> This get's you an archive synced as it's made (as long as streamrecv
> is running), and my "verify"archive command would make sure that if
> for some reason, the backup archive went "down", the wal segments
> would be blocked on the master until it's up again and current.

That's exactly the method I was envisionning, and in fact that I am
using in a couple of cases - jus thaven't documented it properly :)

Since pg_streamrecv only moves a segment into the correct archive
location when it's completed, the archive_command only needs to check
if the file *exists* - if it does, it's transferred, if not, it
returns an error to make sure the wal segments don't get cleaned out.

-- 
 Magnus Hagander
 Me: http://www.hagander.net/
 Work: http://www.redpill-linpro.com/

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