[elephant-devel] Postmodern performance question

[Alex Mizrahi]

 RS> I'm wondering does anyone have any tips on setting up postgres as a
 RS> postmodern backend for Elephant. I suspect that my issues are just a
 RS> case of not really having enough memory for my data set, but if
 RS> there's anything obvious I should be doing, I might as well do that
 RS> first.

it is a good idea to enable logging in postgres to see query execution
durations. normally you would see something on order of 0.01-0.1 ms. if
it takes longer, perhaps it requires tuning.

one of issues i've noticed is that postgresql's planner sometimes
prefers hash joins to normal ones, and this causes problems when
looking up values on large indices in elephant -- even if you lookup
small range it will try to load whole index in memory. if it does so,
it makes sense disabling hash joins, or tuning planner's stats
(e.g. making random IO less costly).