Re: Allowing WAL fsync to be done via O_SYNC

Added to TODO:

* Determine optimal fdatasync/fsync, O_SYNC/O_DSYNC options
* Allow multiple blocks to be written to WAL with one write()

> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > It is hard for me to imagine O_* being slower than fsync(),
>
> Not hard at all --- if we're writing multiple xlog blocks per
> transaction, then O_* constrains the sequence of operations more
> than we really want. Changing xlog.c to combine writes as much
> as possible would reduce this problem, but not eliminate it.
>
> Besides, the entire object of this exercise is to work around
> an unexpected inefficiency in some kernels' implementations of
> fsync/fdatasync (viz, scanning over lots of not-dirty buffers).
> Who's to say that there might not be inefficiencies in other
> platforms' implementations of the O_* options?
>
> regards, tom lane
>

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