Re: Creating indexes?

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,
isit 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
bothfields 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@2ndQuadrant.com   www.2ndQuadrant.us