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Re: pgsql: Document that a CHECKPOINT before taking a file system snapshot

From: Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
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 01:59:04
Message-ID: AANLkTi=d_S73pJxeqBtsFBZN+4Wqp4JE5fvs2md35NpL@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-committerspgsql-hackers
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 ?


>
> Branch
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> Details
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> http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=7276ab5888d85782d988fc297ad2e176c7ad1bca
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> Modified Files
> --------------
> doc/src/sgml/backup.sgml |    2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
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-- 
Cédric Villemain               2ndQuadrant
http://2ndQuadrant.fr/     PostgreSQL : Expertise, Formation et Support

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