Re: Simplifying wal_sync_method

Bruce Momjian <pgman@candle.pha.pa.us> writes:
> 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.

Because there are so many platforms with different subsets of these APIs
and different performance characteristics for the ones they do have.

> It seems 'fsync' should be fdatasync(), and if that is not available,
> fsync().

I have yet to see anyone do any systematic testing of the different
options on different platforms.  In the absence of hard data, proposing
that we don't need some of the options is highly premature.

> In fact, 8.1 uses O_DIRECT if available,

That's a decision that hasn't got a shred of evidence to justify
imposing it on every platform.
        regards, tom lane