Curt Sampson wrote:
> > > Some systems, like Solaris, allow you to turn off the
> > > disk cache, so the problem may not be one you face.)
> >
> > I think it would be interesting to investigate disabling the OS' cache
> > for all relation I/O (i.e. heap files, index files). That way we could
> > both improve performance (by moving all the caching into PostgreSQL's
> > domain, where there is more room for optimization)...
>
> I'm not so sure that there is that all much more room for optimization.
> But take a look at what Solaris and FFS do now, and consider how much
> work it would be to rewrite it, and then see if you even want to do that
> before adding stuff to improve performance.
We need free-behind for large sequential scans, like Solaris has. Do we
have LRU-2 or LRU-K now?
> > If so, is it portable?
>
> O_DIRECT is not all that portable, I don't think. Certainly not as
> portable as mmap.
As I remember, DIRECT doesn't return until the data hits the disk
(because there is no OS cache), so if you want to write a page so you
can reused the buffer, DIRECT would be quite slow.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
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