2016-01-13 16:18 GMT+01:00 Albe Laurenz <laurenz.a...@wien.gv.at>: > 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. >
yes, I though about it too - it is simple, and almost deterministic Pavel > > Yours, > Laurenz Albe >
