On 19.12.2011 21:27, Robert Haas wrote:
To put this another way, we currently WAL-log just about everything. We get away with NOT WAL-logging some things when we don't care about whether they make it to disk. Hint bits, killed index tuple pointers, etc. cause no harm if they don't get written out, even if some other portion of the same page does get written out. But as soon as you CRC the whole page, now absolutely every single bit on that page becomes critical data which CANNOT be lost. IOW, it now requires the same sort of protection that we already need for our other critical updates - i.e. WAL logging. Or you could introduce some completely new mechanism that serves the same purpose, like MySQL's double-write buffer.
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... -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
