Re: Is full_page_writes=off safe in conjunction with

On Sat, 2006-04-15 at 11:45 -0400, Tom Lane wrote:
> 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.

I can see the danger of which you speak, but does it necessarily apply
to all forms of backup?

> > 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?

It seems that we should write an API to allow a backup device to ask for
blocks from the database.

--
Simon Riggs
EnterpriseDB http://www.enterprisedb.com/