Re: Avoiding bad prepared-statement plans.

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