Simplifying wal_sync_method

Currently, here are the options available for wal_sync_method:

#wal_sync_method = fsync # the default varies across platforms:
# fsync, fdatasync, fsync_writethrough,
# open_sync, open_datasync

I don't understand why we support so many values. It seems 'fsync'
should be fdatasync(), and if that is not available, fsync(). Same with
open_sync and open_datasync.

In fact, 8.1 uses O_DIRECT if available, and I don't see why we don't
just use the "data" options automatically if available too, rather than
have users guess which options their OS supports. We might need an
option to print the actual features used, but I am not sure.

Is this something for 8.1 or 8.2?

--
Bruce Momjian | http://candle.pha.pa.us
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