Le 3 février 2012 19:48, Robert Haas <robertmhaas@xxxxxxxxx> a écrit : > 2012/1/22 Tomas Vondra <tv@xxxxxxxx>: >> That's suspiciously similar to the checkpoint timeout (which was set to >> 4 minutes), but why should this matter for minimal WAL level and not for >> archive? > > I went through and looked at all the places where we invoke > XLogIsNeeded(). When XLogIsNeeded(), we: > > 1. WAL log creation of the _init fork of an unlogged table or an index > on an unlogged table (otherwise, an fsync is enough) > 2. WAL log index builds > 3. WAL log changes to max_connections, max_prepared_xacts, > max_locks_per_xact, and/or wal_level > 4. skip calling posix_fadvise(POSIX_FADV_DONTNEED) when closing a WAL file > 5. skip supplying O_DIRECT when writing WAL, if wal_sync_method is > open_sync or open_datasync > 6. refuse to create named restore points > 7. WAL log CLUSTER > 8. WAL log COPY FROM into a newly created/truncated relation > 9. WAL log ALTER TABLE .. SET TABLESPACE > 9. WAL log cleanup info before doing an index vacuum (this one should > probably be changed to happen only in HS mode) > 10. WAL log SELECT INTO > > It's hard to see how generating more WAL could cause a performance > improvement, unless there's something about full page flushes being > more efficient than partial page flushes or something like that. But > none of the stuff above looks likely to happen very often anyway. But > items #4 and #5 on that list like things that could potentially be > causing a problem - if WAL files are being reused regularly, then > calling POSIX_FADV_DONTNEED on them could represent a regression. It > might be worth compiling with POSIX_FADV_DONTNEED undefined and see > whether that changes anything. it should be valuable to have the kernel version and also confirm the same behavior happens with XFS. > > -- > Robert Haas > EnterpriseDB: http://www.enterprisedb.com > The Enterprise PostgreSQL Company > > -- > Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-performance -- Cédric Villemain +33 (0)6 20 30 22 52 http://2ndQuadrant.fr/ PostgreSQL: Support 24x7 - Développement, Expertise et Formation -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
