Re: For the ametures. (related to "Are we losing momentum?")

Ben Clewett <B.Clewett@roadrunner.uk.com> writes:


> > So does PostgreSQL (pg_dump/pg_dumpall).
> 
> I have used this, and it's a great command.
> 
> I could not work out from the documentation whether it takes a
> snapshot at the start time, or archives data at the time it find's it.
> The documentation (app-pg-dump.html).  As the documentation does not
> clarify this very important point, I desided it's not safe to use when
> the system is in use.

Ummm, quoting from the pg_dump manpage:
      pg_dump  makes  consistent backups even if the database is      being used concurrently.  pg_dump  does  not
block other      users accessing the database (readers or writers).
 

What part of this isn't clear?

It's safe.  pg_dump does all its work inside a transaction, so MVCC
rules automatically guarantee that it sees a consistent snapshot.

> Can this command can be used, with users in the system making heavy
> changes, and when takes many hours to complete, does produce a valid
> and consistent backup?

Absolutely.

> If so, you have all MySQL has here and in a more useful format.

I think MySQL's consistent hot backup has to lock tables, while PG's
doesn't...

-Doug