From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com> |
Cc: | pgsql-committers(at)postgresql(dot)org, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: pgsql: Document that a CHECKPOINT before taking a file system snapshot |
Date: | 2010-11-25 03:01:04 |
Message-ID: | 201011250301.oAP314S19309@momjian.us |
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Lists: | pgsql-committers pgsql-hackers |
Cdric Villemain wrote:
> 2010/11/25 Bruce Momjian <bruce(at)momjian(dot)us>:
> > Document that a CHECKPOINT before taking a file system snapshot can
> > reduce recovery time.
>
> I didn't follow that on -hackers, but :
>
> * checkpoint take place in the pg_start_backup process (before it
> releases the hand, so before you can start snapshoting)
>
> * we used to issue a checkpoint *before* pg_start_backup to reduce
> pg_start_backup duration in case you have wal_archiving turn off and
> full_page_write is off, it reduces a bit the IO contention. (or even
> if not I hate seing this pg_start_backup taking seconds/minutes to
> finish)
>
> How the checkpoint before will reduce recovery time ?
This is for using file system snapshots, not PITR or continuous
archiving. The checkpoint reduces how much WAL has to be replayed.
--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ It's impossible for everything to be true. +
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