Streaming replication document

Hi,

There is a description about streaming replication in the doc:
----------------------------------------------------------
25.2.5. Streaming Replication

:
:
If you set up a WAL archive that's accessible from the
standby, wal_keep_segments is not required as the standby can always
use the archive to catch up.
----------------------------------------------------------

I think this description is somewhat inadequate. Since recovery using
WAL archive is file based, it may cause long replication delay. I
think even if WAL archive is set up, we should set wal_keep_segments
to proper value, not 0. Recovery from WAL archive should be the last
resort, shouldn't be?
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

On 04.12.2010 04:18, Tatsuo Ishii wrote:
> There is a description about streaming replication in the doc:
> ----------------------------------------------------------
> 25.2.5. Streaming Replication
>
> :
> :
> If you set up a WAL archive that's accessible from the
> standby, wal_keep_segments is not required as the standby can always
> use the archive to catch up.
> ----------------------------------------------------------
>
> I think this description is somewhat inadequate. Since recovery using
> WAL archive is file based, it may cause long replication delay. I
> think even if WAL archive is set up, we should set wal_keep_segments
> to proper value, not 0. Recovery from WAL archive should be the last
> resort, shouldn't be?

If your standby falls behind that much, catching up is going to take a
while anyway. The master always keeps 2-3 * checkpoint_segments WAL
segments around anyway even if wal_keep_segments is 0.

Depending on the archive, it might well be faster to catch up using the
archive, instead of streaming from master.

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