Re: Free WAL caches on switching segments

daveg wrote:
> On Mon, Feb 13, 2006 at 02:59:43PM -0500, Bruce Momjian wrote:
> > Tom Lane wrote:
> > > Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > > > Tom Lane wrote:
> > > >> More to the point, the utility of the patch remains unproven.
> > > >> We are not in the habit of adding OS dependencies on speculation.
> > >
> > > > He ran tests, though it is speculation because non-caching is a pretty
> > > > hard thing to find a benefit from except under low memory situations.
> > >
> > > Well, the tests (a) didn't show any particularly good speedup, and
> > > (b) were not on the platforms that this is speculated to be useful on
> > > (ie, those without O_DIRECT).
> > >
> > > I really don't think that an adequate case has been made for adding
> > > a new OS dependency.
> >
> > Well, I think the patch should be applied, and the submitter does too,
> > so unless I hear other votes, it is going in.
>
> I vote no for whatever that is worth. A "performance" change needs to
> actually demonstrate improved performance. If the change is really
> desireable to clean up some messy code, then add it as a cleanup change
> without the extra system calls. Otherwise it just adds one more bit of
> mystery for future maintainers who may be decieved into thinking that posix
> advise calls are important voodoo.

Yes, your vote counts very much. What if I apply the patch, but mark
the posix_advise() call in a NOT_USED macro block, so it will be ready
for people to test, but will not be used until we are sure.

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