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Re: Synchronous replication

Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

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From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2010-07-16T10:43:50Z
Lists: pgsql-hackers 
On 16/07/10 10:40, Fujii Masao wrote:
> So we should always prevent the standby from applying any WAL in pg_xlog
> unless walreceiver is in progress. That is, if there is no WAL available
> in the archive, the standby ignores pg_xlog and starts walreceiver
> process to request for WAL streaming.

That completely defeats the purpose of storing streamed WAL in pg_xlog 
in the first place. The reason it's written and fsync'd to pg_xlog is 
that if the standby subsequently crashes, you can use the WAL from 
pg_xlog to reapply the WAL up to minRecoveryPoint. Otherwise you can't 
start up the standby anymore.

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