Re: pg_start_backup without checkpoint patch (a part of Synch Rep)

Fujii Masao wrote:
> Attached is the self-contained patch to skip checkpoint at pg_start_backup.
> This is a part of Synch Rep patches, and was discussed in the following
> thread.
> http://archives.postgresql.org/message-id/3f0b79eb0812240710j7e613f3atfd6b6fc27403546e@mail.gmail.com

I'm not convinced that this is necessary for the replication patch. It
is an orthogonal, new feature, and should be considered for 8.5, IMHO.

> Specifically, pg_start_backup uses the last checkpoint instead of doing a
> new checkpoint if full_page_writes = on since the last checkpoint, which
> guarantees that all the full-pages required for PITR are written.

That assumes that the DBA has kept all the WAL segments that have been
archived since last checkpoint. So this would no longer be safe:

1. rm <archivedir>/*
2. SELECT pg_start_backup();
3. tar cvzf backup.tar.gz <datadir>
4. SELECT pg_stop_backup();

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