On 02/26/2010 03:11 PM, Yeb Havinga wrote:
Tom Lane wrote:
Right, but if the parameter is unknown then its distribution is also
unknown. In any case that's just nitpicking, because the solution is
to create a custom plan for the specific value supplied. Or are you
suggesting that we should create a way for users to say "here is the
expected distribution of this parameter", and then try to fold that into
the planner estimates?
Or instead of letting users give the distribution, gather it
automatically in some plan statistics catalog? I suspect in most
applications queries stay the same for months and maybe years, so
after some number of iterations it is possible to have decent call
statistics / parameter distributions. Maybe the the parameter value
distribution could even be annotated with actual cached plans.
The problem with the last - actual cached plans - is that it implies the
other aspect I have been suggesting: In order to have a custom cached
plan, the primary model must be to use custom plans. If PREPARE/EXECUTE
uses generic plans normally, than the only cached plans available will
be generic plans.
Cheers,
mark
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