no easy answer (was Re: [PLUG] MySQL v. PostgreSQL -- perhaps an easy answer)

Felix Lee felix.1 at canids.net
Thu Jan 15 16:32:02 UTC 2004


Kyle Hayes <kyle at silverbeach.net>:
> We repeatedly evaluated Postgres and stuck with MySQL because we
> kept finding that Postgres docs said that until the DB was down,
> the data on disk wasn't coherent :-( If this has changed, I'd
> love to know about it.  There appeared to be nothing like FLUSH
> TABLES that actually gave us a coherent disk image of the data.

I think you're misreading the docs.
   http://developer.postgresql.org/docs/postgres/backup-file.html
says a normal snapshot of the entire data directory will work.
Restoring from that is the same as if the system had crashed at
that point, which should be fine since that's what databases are
designed to handle.  (ie, all committed transactions will be
done, no uncommitted transactions will be done.)

This seems to me the same thing that goes on if you use the
mysql/innodb hot backup tool, right?

The caveats in the postgres manual seem to be about discouraging
cheating.  You can't just back up selected files, you have to
back up the entire data directory for database integrity.  Well,
I'm guessing you could identify a minimal subset of data that
needs to be backed up (besides an sql-dump), but it looks to me
like postgres wants the freedom to change the storage format
across versions, and to do that you need to discourage people
from working under the hood too much.
--




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