Andreas Pflug
Josh Berkus wrote:
Related to the above, what I don't see in your paper or the proposed
API
is a
way to coordinate full back-ups and WAL archiving. Obviously, the
PITR
Archive is only useful in reference to an existing full backup, so it
is
important to be able to associate a set of PITR archives with a
particular
full backup, or with some kind of "backup checkpoint". I'm sure
that
you
have a solution for this, I just didn't see it explained in your
proposal, or
didn't understand it.
AFAICS there is a small detail
missing so far.

When I'm doing a file level hot backup, I can't be sure about the backup
order. To be sure the cluster is in a consistent state regarding
checkpoints, pg_clog must be the first directory backed up. If this
isn't made sure, the situation could arise that the backed up clog
version contains a checkpoint which marks a transaction completed that
has been written to a file which was backed up earlier than the data
write took place.

This could be insured by doing the backup in two steps; first backing up
pg_clog, and then the rest, restore being performed in the opposite
order.
Good spot. I'll add this to the design.

Will think more on the "backup checkpoint". Don't let me off the hook...

Best Regards, Simon

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