On Mon, Sep 7, 2015 at 8:55 AM, Jayadevan M <maymala.jayade...@gmail.com> wrote:
> Hello , > > I have a parent table and 6 child tables (partitions). The child tables > have check constraints defined in the form > CHECK (myuid in (123,456,..)). > myuid is bigint, the constraints for the 6 child tables are definitely > mutually exclusive. The number of values in the list ranges from 2-10 for 5 > of the child tables. For the 6th child table, the list is 2500+ elements. > When I try explain/explain analyze for even a simple query like > > select * from parent where myuid in (123,456,789) > > the child table with 2500+ elements gets always scanned. I have an index > on the column and that does get used. But why doesn't the planner just use > constraint exclusion and not go for the index scan? Anyone faced a similar > issue? > > IIRC The planner doesn't understand overlaps so having a definition of: IN (1,2,3,4,5); or nearly equivalently = ANY(ARRAY[1,2,3,4,5])) and a request for: IN (1,3,5) / = ANY(ARRAY[1,3,5]) is going to get you nowhere with the planner. I am not sure but am doubting it is intelligent enough to recognize the functional expression even if all of the values are present. "simple equality" ( http://www.postgresql.org/docs/9.4/interactive/ddl-partitioning.html) this is not. David J.
