At 12:38 PM 4/13/2007, Steve wrote:
Really?
Wow!
Common wisdom in the past has been that values above a couple of hundred
MB will degrade performance. Have you done any benchmarks on 8.2.x that
show that you get an improvement from this, or did you just take the
"too much of a good thing is wonderful" approach?
Not to be rude, but there's more common wisdom on this
particular subject than anything else in postgres I'd say ;) I
think I recently read someone else on this list who's
laundry-listed the recommended memory values that are out there
these days and pretty much it ranges from what you've just said to
"half of system memory".
I've tried many memory layouts, and in my own experience
with this huge DB, more -does- appear to be better but marginally
so; more memory alone won't fix a speed problem. It may be a
function of how much reading/writing is done to the DB and if fsync
is used or not if that makes any sense :) Seems there's no "silver
bullet" to the shared_memory question. Or if there is, nobody can
agree on it ;)
One of the reasons for the wide variance in suggested values for pg
memory use is that pg 7.x and pg 8.x are =very= different beasts.
If you break the advice into pg 7.x and pg 8.x categories, you find
that there is far less variation in the suggestions.
Bottom line: pg 7.x could not take advantage of larger sums of memory
anywhere near as well as pg 8.x can.
Cheers,
Ron
