Slow query on “UNION ALL” view

Question

I have a DB view which basically consists of two SELECT queries with UNION ALL, like this:

CREATE VIEW v AS
SELECT time, etc. FROM t1 /         


        

Answer 1

This seems to be a case of a pilot error. The "v" query plan selects from at least 5 different tables.

Now, Are You sure You are connected to the right database? Maybe there are some funky search_path settings? Maybe t1 and t2 are actually views (possibly in a different schema)? Maybe You are somehow selecting from the wrong view?

Edited after clarification:

You are using a quite new feature called "join removal" : http://wiki.postgresql.org/wiki/What%27s_new_in_PostgreSQL_9.0#Join_Removal

http://rhaas.blogspot.com/2010/06/why-join-removal-is-cool.html

It appears that the feature does not kick in when union all is involved. You probably have to rewrite the view using only the required two tables.

another edit: You appear to be using an aggregate (like "select count(*) from v" vs. "select * from v"), which could get vastly different plans in face of join removal. I guess we won't get very far without You posting the actual queries, view and table definitions and plans used...