On Tue, Oct 4, 2016 at 8:05 AM, Chenxi Li <spirit...@gmail.com> wrote: > How is cardinality estimation for "group by" is done and where is the code > doing that?
I would suggest that you start by looking at estimate_num_groups() in src/backend/utils/adt/selfuncs.c. You might also want to look at cost_agg() in src/backend/optimizer/path/costsize.c, and also the places where it gets called. They don't all estimate the number of groups in the same way. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
