On Fri, Apr 30, 2010 at 10:08 AM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Mike Christensen <mike@xxxxxxxxxxxxx> writes: >> When a certain event happens, let's say event 4, I need to query for which >> users to notify. So I'll be doing something like: > >> SELECT UserId FROM Users WHERE Subscriptions & 8; > >> My question is say there's a million rows in the Users table. If I have an >> index on Subscriptions, will this index be used in the above query? > > No. At least not with a standard btree index. > > I'm not exactly sure that an index would be helpful at all --- it seems > like the selectivity of this condition won't be very good anyway, will > it? The more popular notifications will be subscribed to by a large > fraction of the user base. Maybe it'd be useful to index unpopular > notifications, but how often will you be searching for those? > We've got some similar columns (though nothing with any major number of rows), so this is interesting... If all subscriptions are roughly equal in popularity then any single select should give ~ 10% of the data. That would seem to be selective enough that you'd really want an index? If so, any answers to the OP's main question; what would be the most efficient way to handle this type of thing? -- Peter Hunsberger -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
