i tell about wal_level is higher than MINIMAL
wal_level != minimal http://doxygen.postgresql.org/xlogdefs_8h_source.html " 48 * Because O_DIRECT bypasses the kernel buffers, and because we never 49 * read those buffers except during crash recovery or if wal_level != minimal " >> 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
