On 2018-01-09 20:51:17 -0500, Stephen Frost wrote: > Greetings, > > * Andreas Joseph Krogh (andreas@visena.com) wrote: > > Aha, so enabling CRC causes hint-bits to be written causing extra WAL-logging, > > which woudn't be the case without CRC enabled? > > Thanks for pointing that out. > > Yes, having checksums enabled forces logging of hint bits. You can > enable wal_log_hints independently too, without having checksums, to see > what kind of an impact it'll have on your environment. > > A useful documentation update might be: > > --- > With checksums enabled, wal_log_hints <link to the GUC's documentation> > will be enabled and each page read or write will involve calculating the > checksum for the page. > --- > > I'd probably just replace the "Enabling checksums may incur a noticeable > performance penalty" with the above, as it should be clear that doing > more work implies an impact on performance and that avoids the whole > question of trying to characterize in a general way something that can't > be generalized (as it's workload dependent).
