Jeff wrote:

On Fri, 31 Oct 2003 09:31:19 -0600
"Rob Sell" <[EMAIL PROTECTED]> wrote:

Not being one to hijack threads, but I haven't heard of this
performance hit when using HT, I have what should all rights be a
pretty fast server, dual 2.4 Xeons with HT 205gb raid 5 array, 1 gig
of memory. And it is only 50% as fast as my old server which was a
dual AMD MP 1400's with a 45gb raid 5 array and 1gb of ram. I have
read everything I could find on Pg performance tweaked all the
variables that were suggested and nothing. Which is why I subscribed
to this list, just been lurking so far but this caught my eye.

There's benchmarks around that show in _some_ cases HT is not all it is
cracked up to be, somtimes running slower.

To use HT effectively on needs.

1. A kernel that understands HT.
2. A task scheduler that understands HT
3. A CPU intensive load.

So if you are running a stock RedHat and production postgresql database, turn it off. It won't hurt certainly(Almost certainly)

I'm guessing RH is running some useless stuff in the BG.. or maybe he's
running a retarded kernel... or.. maybe.. just.. maybe.. little elves
are doing it.

Too much..:-)

I guess Alexandre can tune bdflush to be little less agressive. Comparing bdflush values on two machines might turn up something.

His idea of compiling kernel is also good one. He can also try tuning some values in /proc/sys/vm but I don't find any documentation offhand.

I usually run slackware and a handcompiled 2.6-test4. None of them use any swap unless true memory starts falling low. This touch-swap-even-if-oodles-of-ram-is-free is something I have't experienced on my desktop for quite a while.


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