| From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
|---|---|
| To: | Fujii Masao <masao(dot)fujii(at)gmail(dot)com> |
| Cc: | Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Synchronous replication |
| Date: | 2010-07-16 10:43:50 |
| Message-ID: | 4C4037E6.1000300@enterprisedb.com |
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| 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
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