Pavel Stehule wrote:
> I like a strategy based on risks. Probably there are situation, when the 
> generic plan is great every
> time - INSERTs, UPDATEs via PK, simple SELECTs via PK. generic plan can be 
> well if almost all data has
> similar probability. Elsewhere on bigger data, the probability of pretty slow 
> plan is higher, and then
> we should to prefer custom plan.
> so the strategy - if cost of generic plan is less than some MAGIC CONSTANT 
> (can be specified by GUC),
> then use generic plan. Elsewhere use a custom plan everytime.
> It allow to controll the plan reusing. When MAGIC CONSTANT = 0 .. use custom 
> plan everytime, When
> MAGIC CONSTANT = M, then use generic plan always.

I have a different idea:

What about a GUC "custom_plan_threshold" that controls after how many
executions a generic plan will be considered, with a default value of 5.

A value of -1 could disable generic plans.

Laurenz Albe

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