-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 11/15/06 14:28, Martijn van Oosterhout wrote: > On Wed, Nov 15, 2006 at 01:41:47PM -0600, Ron Johnson wrote: >> -----BEGIN PGP SIGNED MESSAGE----- >> Hash: SHA1 >> >> 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"). How does it know what a crashed PostgreSQL database look like? Besides, active transactions need to be *rolled back*, not written ahead, since half the data hasn't been sent from the computer yet. - -- Ron Johnson, Jr. Jefferson LA USA Is "common sense" really valid? For example, it is "common sense" to white-power racists that whites are superior to blacks, and that those with brown skins are mud people. However, that "common sense" is obviously wrong. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) iD8DBQFFW3nMS9HxQb37XmcRAn0vAJ996FVUuoBrtiS/B59iU5jkkJxR2ACeM5A8 BE1Bvph5pG0a+uLg9Kc/zwc= =ZwsZ -----END PGP SIGNATURE-----
