Greg Stark <[EMAIL PROTECTED]> writes:
> Plan stability is also an important feature, especially for OLTP
> systems which have hard real-time requirements. OLTP systems typically
> don't care about getting the "best" plan for a query, only a plan that
> is "good enough".
> "Good enough" means it can keep up with the rate of incoming requests; it
> doesn't matter whether it keeps up with 10% headroom or 20% headroom. But if
> one incoming query even one in a thousand takes 1000% of the time available
> then the entire system risks falling down.
Is it worth pointing out that using the same plan all the time is *no*
recipe for guaranteeing response time? There is no such thing as a plan
that is good for every case --- outlying data values can make a
usually-good plan blow out your performance guarantee anyway. Disabling
the planner is just a recipe for ensuring that that will happen, IMHO.
regards, tom lane
---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match
