Re: Page Checksums
Jim Nasby <jim@nasby.net>
From: Jim Nasby <jim@nasby.net>
To: Simon Riggs <simon@2ndquadrant.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>, Robert Haas <robertmhaas@gmail.com>, David Fetter <david@fetter.org>, Stephen Frost <sfrost@snowman.net>, Aidan Van Dyk <aidan@highrise.ca>, Josh Berkus <josh@agliodbs.com>, pgsql-hackers@postgresql.org, Greg Smith <greg@2ndQuadrant.com>, Koichi Suzuki <koichi.szk@gmail.com>
Date: 2012-01-10T00:12:06Z
Lists: pgsql-hackers
On Jan 8, 2012, at 5:25 PM, Simon Riggs wrote: > On Mon, Dec 19, 2011 at 8:18 PM, Heikki Linnakangas > <heikki.linnakangas@enterprisedb.com> wrote: > >> Double-writes would be a useful option also to reduce the size of WAL that >> needs to be shipped in replication. >> >> Or you could just use a filesystem that does CRCs... > > Double writes would reduce the size of WAL and we discussed many times > we want that. > > Using a filesystem that does CRCs is basically saying "let the > filesystem cope". If that is an option, why not just turn full page > writes off and let the filesystem cope? I don't think that just because a filesystem CRC's that you can't have a torn write. Filesystem CRCs very likely will not happen to data that's in the cache. For some users, that's a huge amount of data to leave un-protected. Filesystem bugs do happen... though presumably most of those would be caught by the filesystem's CRC check... but you never know! -- Jim C. Nasby, Database Architect jim@nasby.net 512.569.9461 (cell) http://jim.nasby.net