On Wed, Oct 15, 2008 at 10:42 AM, Bill Thoen <bthoen@xxxxxxxxxx> wrote: > Does PG (8.1) ever use existing indexes when executing an UPDATE? > > I've got some tables with millions of records and whenever I update a column > that involves most or all the records the EXPLAIN command seems to indicate > that it isn't using the pre-existing indexes. This result in a slow update, > which is further slowed by the presence of indexes. So when doing a large > update should I just drop the indexes first, or is there some good reason to > keep them? > > Thanks, > - Bill Thoen You have to hit the disk twice if you use an index -- once to read the index and once to read the table itself. If the planner guesses that an operation involves most of the records in a table, it will avoid indexes and just seqscan, because it's faster. - Josh / eggyknap -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
