Hi, On Mon, Dec 29, 2008 at 6:08 PM, Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> wrote: > 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/3f0b79eb0812240710j7e613f3atfd6b6fc274035...@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.
Synch Rep forces online-backup in some scenes (e.g. catchup after failover), so I've argued from the beginning that the cost of it should be reduced. I think this patch is one of the solutions to that problem. > >> 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(); Umm... I can't believe that there is the DBA to carry out such unsafe operation. If disk crash occurs between 1 and 2, a database might not recover *regardless of this patch* because of some missing xlogs. I don't think that the patch itself is unsafe. In this patch, the DBA can still judge safely which file can be removed, from a backup history file or the return value of pg_start_backup. Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
