On Tue, 2010-04-20 at 21:03 -0400, Tom Lane wrote: > Simon Riggs <si...@2ndquadrant.com> writes: > > Following patch writes a new WAL record that just says "copy foo to > > newts" and during replay we flush buffers and then re-execute the copy > > (but only when InArchiveRecovery). So the copy happens locally on the > > standby, not copying from primary to standby. We do this just with a > > little refactoring and a simple new WAL message. > > And what happens to crash-recovery replay? You can't have it both ways, > either the data is in WAL or it's missing.
The patch changes nothing in the case of crash recovery. There is no WAL written if !XLogIsNeeded, so we *must* have already made the decision that the absence of WAL is not a problem for crash recovery. Note that currently we flush the new table to disk just like we do for heap_sync(), whether or not WAL is written. > > Objections? > > This is NOT the time to be rushing in marginal performance > optimizations. I don't think you've thought through all the corner > cases anyway. The performance gain isn't marginal, otherwise I wouldn't have bothered writing it * We avoid writing GB of unnecessary WAL data on primary * We avoid streaming that WAL data to the standby If you can see a corner case that I do not, please say. -- Simon Riggs www.2ndQuadrant.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
