Andrew,
> I think the "25%" rule of thumb is slightly stale: above some
> threshold, it just falls apart, and lots of people now have machines
> well within that threshold. Heck, I'll bet Bruce's 2-way machine is
> within that threshold.
Sure. But we had a few people on this list do tests (including me) and the
anecdotal evidence was lower than 25%, substantially. The falloff is subtle
until you hit 50% of RAM, like:
% query throughput
1 ----
5 ---------
10 -----------
15 ----------
20 ----------
25 ---------
30 --------
35 --------
40 -------
... so it's often not immediately apparent when you've set stuff a little too
high. However, in the folks that tested, the ideal was never anywhere near
25%, usually more in the realm of 5-10%. I've been using 6% as my starting
figure for the last year for a variety of servers with good results.
Of course, if you have anecdotal evidence to the contrary, then the only way
to work this would be to have OSDL help us sort it out.
--
-Josh Berkus
Aglio Database Solutions
San Francisco