On Mon, Jul 27, 2009 at 3:15 PM, Zach Conrad<zach.conrad@digitecinc.com> wrote:
> While creating a function, I kept getting a large variance in runtime between the raw query vs. using the
function/preparedstatement. After talking with folks on #postgresql, specifically David Fetter, he thought I should
mentionit here.
When you PREPARE with a parameter, it generates the plan without
knowing specifically which value you intend to substitute at execution
time. Obviously, this can affect what plan gets chosen, because it's
sort of trying to make a best guess without knowing whether the actual
value will be a common one or an uncommon one. I bet if you PREPARE
it without the parameter, you'll get the same plan as executing it
directly.
...Robert
