On 2013-04-12 15:31:36 -0400, Bruce Momjian wrote: > On Fri, Apr 12, 2013 at 09:28:42PM +0200, Andres Freund wrote: > > > Only point worth discussing is that this change would make backup blocks > > > be > > > covered by a 16-bit checksum, not the CRC-32 it is now. i.e. the record > > > header is covered by a CRC32 but the backup blocks only by 16-bit. > > > > That means we will have to do the verification for this in > > ValidXLogRecord() *not* in RestoreBkpBlock or somesuch. Otherwise we > > won't always recognize the end of WAL correctly. > > And I am a bit wary of reducing the likelihood of noticing the proper > > end-of-recovery by reducing the crc width. > > > > Why again are we doing this now? Just to reduce the overhead of CRC > > computation for full page writes? Or are we forseeing issues with the > > page checksums being wrong because of non-zero data in the hole being > > zero after the restore from bkp blocks? > > I thought the idea is that we were going to re-use the already-computed > CRC checksum on the page, and we only have 16-bits of storage for that.
Well, but the proposal seems to be to do this also for non-checksum enabled datadirs, so ... Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers