Paul Tuckfield wrote: > I really like the idea of taking a snapshot backup with postgres, using > either volume manager or hardware splits in a disk array to get a > physical backup. > > In other, lesser database systems :) the system is structured to prevent > problems arising from "split block" writes, meaning that though the > database is writing an 8k block at the instant of the split, the > intervening drivers may have written a partial block. two ways to > avoid this problem, as I understand, are: > > 1.) freeze all block writes briefly (excluding WAL perhaps). > Q:) I saw a patch going out to do writes in a background process. is > this only to help write blocks before absolutely necessary, or is it to > do *all* writes? if so, this would make adding freeze logic simple > > 2.) enable logging of entire blocks to the WAL, so recovery can > overwrite any partial blocks caught writing at the instant of split. > Q.) Does the WAL write tuple-level changes or block-level changes.
We write entire 8k pages to WAL on first modify so we can recover from partial 8k writes. -- Bruce Momjian | http://candle.pha.pa.us [EMAIL PROTECTED] | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 ---------------------------(end of broadcast)--------------------------- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faqs/FAQ.html
