J. R. Nield wrote:
> So since we have all this buffering designed especially to meet our
> needs, and since the OS buffering is in the way, can someone explain to
> me why postgresql would ever open a file without the O_DSYNC flag if the
> platform supports it?
We sync only WAL, not the other pages, except for the sync() call we do
during checkpoint when we discard old WAL files.
> > I concur with Bruce: the reason we keep page images in WAL is to
> > minimize the number of places we have to fsync, and thus the amount of
> > head movement required for a commit. Putting the page images elsewhere
> > cannot be a win AFAICS.
>
>
> Why not put all the page images in a single pre-allocated file and treat
> it as a ring? How could this be any worse than flushing them in the WAL
> log?
>
> Maybe fsync would be slower with two files, but I don't see how
> fdatasync would be, and most platforms support that.
We have fdatasync option for WAL in postgresql.conf.
-- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610)
853-3000+ If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill,
Pennsylvania19026
