> > Yes, this double-writing is a problem. Suppose you have your WAL on a
> > separate drive. You can fsync() WAL with zero head movement. With a
> > log based file system, you need two head movements, so you have gone
> > from zero movements to two.
>
> It may be worse depending on how the filesystem actually does
> journalling. I wonder if an fsync() may cause ALL pending
> meta-data to be updated (even metadata not related to the
> postgresql files).
>
> Do you know if reiser or xfs have this problem?
I don't know, but the Linux user reported xfs was really slow.
--
Bruce Momjian | http://candle.pha.pa.us
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+ If your life is a hard drive, | 830 Blythe Avenue
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