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@candle.pha.pa.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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