Re: RE: [COMMITTERS] pgsql/src/backend/access/transam ( xact.c xlog.c)

* Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> [001116 12:31] wrote:
> > > In OS kernel design, you try to avoid process herding bottlenecks.
> > > Here, we want them herded, and giving up the CPU may be the best way to
> > > do it.
> >
> > Yes, but if everyone yeilds you're back where you started, and with
> > 128 or more backends do you really want to cause possibly that many
> > context switches per fsync?
>
> You are going to kernel call/yield anyway to fsync, so why not try and
> if someone does the fsync, we don't need to do it. I am suggesting
> re-checking the need for fsync after the return from sleep(0).

It might make more sense to keep a private copy of the last time
the file was modified per-backend by that particular backend and
a timestamp of the last fsync shared globally so one can forgo the
fsync if "it hasn't been dirtied by me since the last fsync"

This would provide a rendevous point for the fsync call although
cost more as one would need to periodically call gettimeofday to
set the modified by me timestamp as well as the post-fsync shared
timestamp.

--
-Alfred Perlstein - [bright(at)wintelcom(dot)net|alfred(at)freebsd(dot)org]
"I have the heart of a child; I keep it in a jar on my desk."