On Thu, Oct 7, 2010 at 10:52 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Josh Berkus <j...@agliodbs.com> writes: >> I thought we fixed this in 8.4.4, but apparently not. In the event that >> you have a GIN index containing a WHERE clause which is sufficiently >> restrictive, PostgreSQL will attempt to use the index even though it >> can't. > > We could probably kluge the planner to avoid that case, but in view > of the other issues explained here: > http://developer.postgresql.org/pgdocs/postgres/gin-limit.html > I'm not sure it's worth the trouble. There's nothing the planner can do > to guard against the equivalent issue of non-restrictive queries, ie > there is a WHERE clause but it's something like "array-column contains > empty-array". The fact that the comparison value is empty might not be > known until runtime. > > IMO, what's needed is to fix GIN so it doesn't go insane for empty > values or non-restrictive queries, by ensuring there's at least one > index entry for every row. This has been discussed before; see the TODO > section for GIN.
That seems like it could waste an awful lot of disk space (and therefore I/O, etc.). No? -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
