Generally speaking, once you've gotten to the point of swapping, even a
little, you've gone too far. A better approach is to pick some
conservative number, like 10-25% of your ram for shared_buffers, and 1
gig or so for maintenance work_mem, and then increase them while
exercising the system, and measure the difference increasing them makes.
If going from 1G shared buffers to 2G shared buffers gets you a 10%
increase, then good. If going from 2G to 4G gets you a 1.2% increase,
it's questionable. You should reach a point where throwing more
shared_buffers stops helping before you start swapping. But you might
not.
Same goes for maintenance work mem. Incremental changes, accompanied by
reproduceable benchmarks / behaviour measurements are the way to
determine the settings.
Note that you can also vary those during different times of the day.
you can have maint_mem set to 1Gig during the day and crank it up to 8
gig or something while loading data. Shared_buffers can't be changed
without restarting the db though.
I'm currently benchmarking various configuration adjustments. Problem is
these tests take a really long time because I have to run the load
process... which is like a 9 hour deal. That's why I'm asking for advice
here, because there's a lot of variables here and it's really time costly
to test :)
I'm still working on the benchmarkings and by Friday I should have some
interesting statistics to work with and maybe help figure out what's going
on.
Thanks!
Steve
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