On 07/21/2013 10:01 PM, Миша Тюрин wrote: > hi, list. there are my proposal. i would like to tell about odirect in wal > sync in wal_level is higher than minimal. i think in my case when wal traffic > is up to 1gb per 2-3 minutes but discs hardware with 2gb bbu cache (or maybe > ssd under wal) - there would be better if wall traffic could not harm os > memory eviction. and i do not use streaming. my archive command may read wal > directly without os cache. just opinion, i have not done any tests yet. but i > am still under the some memory eviction anomaly.
PostgreSQL already uses O_DIRECT for WAL writes if you use O_SYNC mode for WAL writes. See comments in src/include/access/xlogdefs.h (search for O_DIRECT). You should also examine src/backend/access/transam/xlog.c, particularly the function get_sync_bit(...) Try doing some tests with pg_test_fsync, see how performance looks. If your theory is right and WAL traffic is putting pressure on kernel write buffers, using fsync=open_datasync - which should be the default on Linux - may help. I'd recommend doing some detailed tracing and performance measurements before trying to proceed further. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
