Hello, On Thu, Dec 21, 2017 at 6:01 PM, David Rowley <david.row...@2ndquadrant.com> wrote: > On 21 December 2017 at 23:51, Beena Emerson <memissemer...@gmail.com> wrote: >> On Thu, Dec 21, 2017 at 2:31 PM, David Rowley >> <david.row...@2ndquadrant.com> wrote: >>> On 19 December 2017 at 21:54, Beena Emerson <memissemer...@gmail.com> wrote: >> >>> The problem is down to the logic in choose_custom_plan() only choosing >>> a generic plan if the average cost of the generic plan is less than >>> the average custom plan cost. The problem is that the generic plan can >>> have many extra Append subnodes in comparison to the custom plan, all >>> of which are taken into account in the total plan cost, but these may >>> be pruned during execution. The logic in choose_custom_plan() has no >>> idea about this.. >> >> I had mentioned this in the first mail on this thread that the generic >> plan is always preferred and Robert said that it is not in scope of >> this patch. Maybe we can start a new thread for this. > > Sorry, I missed that. I knew you had modified choose_custom_plan() > too, but I didn't know the diagnosis of the problem had made its way > here yet. > > I wonder if Robert understands the extent of the problem. The patch > will be useful to prune away partitions when the partitioned table is > on the inside of a parameterised nested loop join, but I think we'll > likely get some complaints about PREPARE statements always using a > custom plan. It's going to make this pretty hard to write regression > tests for unless we went and invent some GUC "prefer_generic_plan", or > "generic_plan_cost_multiplier" to provide a way to coax > choose_custom_plan() into not choosing a custom plan. I admit to not > having the answer to this but I don't think we should rule out > discussing possible fixes.
I have attached the regression tests I am currently using to check my patch. It has few prepared statements using runtime pruning. -- Beena Emerson EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
runtime_pruning_testcases.patch
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