Re: Is full_page_writes=off safe in conjunction with PITR?

Bruce Momjian <pgman ( at ) candle ( dot ) pha ( dot ) pa ( dot ) us> writes:
> > I am thinking we should throw an error on pg_start_backup() and
> > pg_stop_backup if full_page_writes is off.
> 
> No, we'll just change the test in xlog.c so that fullPageWrites is
> ignored if XLogArchivingActive.
> 
> > Seems archive_command and
> > full_page_writes can still be used if we are not in the process of doing
> > a file system backup.
> 
> Think harder: we are only safe if the first write to a given page after
> it's mis-copied by the archiver is a full page write.  The requirement
> therefore continues after pg_stop_backup.  Unless you want to add
> infrastructure to keep track for *every page* in the DB of whether it's
> been fully written since the last backup?

I am confused.  Since we checkpoint during pg_start_backup(), isn't any
write to a file while the tar backup is going on going to be a full page
write?  And once we pg_stop_backup(), do we need full page writes?

--  Bruce Momjian   http://candle.pha.pa.us EnterpriseDB    http://www.enterprisedb.com
 + If your life is a hard drive, Christ can be your backup. +