Bjørn T Johansen wrote:
What is the best approach for PostgreSQL when creating indexes? E.g I have two fields in a table that I want indexed, is it best to create one index combining the two fields or creating one for each field? If I create one for each field, will the search when using both fields be slower that a combined index?
http://www.postgresql.org/docs/current/static/indexes-bitmap-scans.html covers the basis here. There is some amount of additional overhead in keeping around and using two indexes on a single field as opposed to one two-field index, particularly in terms of disk space used. However, the result is enormously more flexible. Having two single-column indexes can satisfy all sorts of queries that the combined index wouldn't be a help on, and the overhead of combining the index results together is low.
-- Greg Smith 2ndQuadrant US Baltimore, MD PostgreSQL Training, Services and Support greg@xxxxxxxxxxxxxxx www.2ndQuadrant.us -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
