Re: Using SAN Splits to instantly copy a DB

On Wed, Nov 15, 2006 at 01:41:47PM -0600, Ron Johnson wrote:
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> On 11/15/06 09:47, Jim Nasby wrote:
> > On Nov 14, 2006, at 3:44 PM, Paul Silveira wrote:
> [snip]
> > Rule 2 is needed to ensure that the data files in the database are all
> > consistent to each other. If you have a SAN/filesystem with snapshot
> > capability (sounds like you do), then you can do that to create the copy
> > rather than shutting the database down.
>
> How does SAN-snapshot ensure transactional consistency?

There is write-ahead logging to do that. It's the same machanism used
to ensure database consistancy after a crash. When you take a snapshot
and start a new postmaster on the snapshot, it sees what looks like a
crashed database and recovers it to the instant it snapshotted (aka
"crashed").

Have a nice day,
--
Martijn van Oosterhout   <kleptog@svana.org>   http://svana.org/kleptog/
> From each according to his ability. To each according to his ability to litigate.