On Tue, 2007-01-09 at 17:05, tsuraan wrote: > I have a table of messages with paths and inserted dates (among other > things), like so: > > CREATE TABLE Messages ( > msgkey BIGSERIAL PRIMARY KEY, > path TEXT NOT NULL, > inserted TIMESTAMP WITHOUT TIMEZONE DEFAULT NOW() > ); > > I run a query to determine which days actually saw emails come in, > like so: > > SELECT DATE(inserted) FROM Messages GROUP BY DATE(inserted); You're probably under the mistaken impression that PostgreSQL and can retrieve all the data it needs from the index alone. It can't. Anytime postgresql gets an index reference, it has to then visit the actual table file to grab the individual entry. That's because indexes don't store mvcc visibility information, and due to the problems locking both indexes and tables together would present, probably won't any time soon.
