On Wed, Oct 15, 2008 at 8:58 AM, Ivan Voras <ivoras@freebsd.org> wrote:
> 2008/10/15 Aidan Van Dyk <aidan@highrise.ca>:
>> * Ivan Voras <ivoras@freebsd.org> [081015 10:05]:
>>
>>> So, pg_start_backup() freezes the data at the time it's called but still
>>> data and xlog are changed, in a different way that's safe to backup? Why
>>> not run with pg_start_backup() always enabled?
>>
>> I think your missing the whole point of "pg_start_backup()".
>> pg_start_backup()" is *part* of a full PITR/backup run. i.e. you use it
>> when you have an archive command working as well. It's *not* mean tto
>> just allow you to do a filesystem copy inside a running data directory.
>
> Possibly - that's why I'm sticking to this thread :) My context is
> doing full filesystem-only copies/backups of the database (xlogs &
> all) - is pg_start_backup() applicable?
Just an FYI, there are some issues with using filesystems that support
snapshots, depending on the OS / filesystem. For instance, the LVM,
which linux uses that allows snapshots, has issues with write barriers
and also has a maximum throughput of about 300Meg/second. It's all a
trade-off, but I don't run my db files on LVM because of those two
problems.