Re: Avoiding bad prepared-statement plans.

Hi Robert,

On Tue, Feb 9, 2010 at 17:43, Robert Haas <robertmhaas@gmail.com> wrote:

> On Tue, Feb 9, 2010 at 7:08 AM, Jeroen Vermeulen <jtv@xs4all.nl> wrote:
> > = Projected-cost threshold =
> >
> > If a prepared statement takes parameters, and the generic plan has a high
> > projected cost, re-plan each EXECUTE individually with all its parameter
> > values bound.  It may or may not help, but unless the planner is vastly
> > over-pessimistic, re-planning isn't going to dominate execution time for
> > these cases anyway.
>
> How high is high?
>

Perhaps this could be based on a (configurable?) ratio of observed planning
time and projected execution time. I mean, if planning it the first time
took 30 ms and projected execution time is 1 ms, then by all means NEVER
re-plan. But if planning the first time took 1 ms and resulted in a
projected execution time of 50 ms, then it's relatively cheap to re-plan
every time (cost increase per execution is 1/50 = 2%), and the potential
gains are much greater (taking a chunk out of 50 ms adds up quickly).

Cheers,
Bart