Victor Dobrovolsky <booby.stager@xxxxxxxxx> writes: > It is clear that for immutable/stable functions with constant parameters, > query planner could/should calculate value in a parse time and use it > directly in query, or at least once per query. Immutable, yes, stable, no. Awhile back there was a draft patch to cache outputs of stable functions after running them once in a query, but I don't think anyone's still working on that. IIRC we were having a hard time convincing ourselves that the extra bookkeeping would pay for itself. > But it is unclear for me what exactly should/can happens when parameters > are bounded not to constant values but to query fields. > In such a case there could be some caching mechanics involved for > parameters combinations and result values. > Like building a hash table for that or something similar. No such mechanism exists. Again, there would be a lot of tradeoffs involved and it's difficult to say if it'd be a win. regards, tom lane
