Message-ID: <53D39B93.1030207@2ndquadrant.com>
Date: Sat, 26 Jul 2014 20:14:11 +0800
From: Craig Ringer <craig@2ndquadrant.com>
Organization: 2nd Quadrant
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To: John Scalia <jayknowsunix@gmail.com>,
 "pgsql-admin@postgresql.org" <pgsql-admin@postgresql.org>
Subject: Re: WAL segment management on a standby
References: <53C015AA.5070908@gmail.com> <53C33DE8.7000902@2ndquadrant.com>
 <53C3E1AC.60704@gmail.com>
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On 07/14/2014 09:57 PM, John Scalia wrote:
> 
> First, it whined about no history.0000004 file, which as the last WAL
> segment is 0000000030000000E00000004E, I'm guessing the standby thought
> the timeline might have been changed, but it was not. Then, it
> complained about no history.00000003 file in the archive area. This file
> had already been copied up into pg_xlog and deleted from the archive.

No immediate answer for you there.

> Finally, the last complaint was that it couldn't find
> 0000000030000000E00000004F in the archive. It appears that under
> streaming a standby server will write concurrently with the primary any
> WAL segment the primary is still generating. I say this as that missing
> WAL segment ("...4F") was already in the pg_xlog directory, but it
> hadn't yet made it into the archive area. Eventually, 10 minutes later,
> 4F did appear in the archive. Is my interpretation here correct, that a
> standby will concurrently write a WAL segment in streaming replication
> mode?

The xlog files get written to in pg_xlog until they're rotated. When
rotated, they get archived; when the archive command completes, they
become accessible to standby servers.

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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