i tell about wal_level is higher than MINIMAL

wal_level != minimal
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
>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
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