Maxim Boguk <maxim.bo...@gmail.com> writes: > Test case look like:
> create table "references" ( attr_id integer, reference integer, > object_id integer ); > insert into "references" select *100**(random()), > *100000**(random()^*10*), *1000000**(random()) from > generate_series(*1*,*10000000*); > create index xif01references on "references" ( reference, attr_id ); > create index xif02references on "references" ( object_id, attr_id, reference > ); > analyze "references"; > explain select * from "references" rs left join "references" vm on > vm.reference = rs.reference and vm.attr_id = *10* where rs.object_id = > *1000*; I don't believe there's actually anything very wrong here. The large-looking estimate for the join size is not out of line: if you try different values for object_id you will find that some produce more rows than that and some produce less. If we had cross-column stats we could maybe derive a better estimate, but as-is you're getting an estimate that is probably about right on the average, depending on whether the particular object_id matches to more common or less common reference values. The thing that looks funny is that the inner indexscan rowcount estimate is so small, which is because that's being done on the assumption that the passed-in rs.reference value is random. It's not really --- it's more likely to be one of the more common reference values --- which is something that's correctly accounted for in the join size estimate but not in the inner indexscan estimate. regards, tom lane -- Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-bugs