GIST versus GIN indexes for intarrays

Hi Guys,

I'm a bit confused when the proper way to use GIST versus GIN indexes
with integer arrays.

The documentation states:

http://www.postgresql.org/docs/current/static/intarray.html

The choice between GiST and GIN indexing depends on the relative
performance characteristics of GiST and GIN, which are discussed
elsewhere. As a rule of thumb, a GIN index is faster to search than a
GiST index, but slower to build or update; so GIN is better suited for
static data and GiST for often-updated data.

Since 100% of my queries are for retrieval, I should use GIN but it
never appears to be used unlike how GIST indexes are:

gearbuyer_ig=# select version();
version
----------------------------------------------------------------------------------------------------
PostgreSQL 8.3.6 on i686-pc-linux-gnu, compiled by GCC gcc (GCC)
4.1.2 20070925 (Red Hat 4.1.2-33)
(1 row)

With just a GIN index I get this plan (no use of GIN):

gearbuyer_ig=# explain select count(*) from items where
items.fast_colors @> ARRAY[0];
QUERY PLAN
-----------------------------------------------------------------
Aggregate (cost=21194.27..21194.28 rows=1 width=0)
-> Seq Scan on items (cost=0.00..21193.64 rows=251 width=0)
Filter: (fast_colors @> '{0}'::integer[])
(3 rows)

With a GIST index created like:

gearbuyer_ig=# CREATE INDEX items_fast_colors_rdtree2_idx ON items
USING gist (fast_colors gist__int_ops);

gearbuyer_ig=# explain select count(*) from items where
items.fast_colors @> ARRAY[0];
QUERY PLAN
-----------------------------------------------------------------------------------------------------
Aggregate (cost=929.81..929.82 rows=1 width=0)
-> Bitmap Heap Scan on items (cost=14.30..929.18 rows=251 width=0)
Recheck Cond: (fast_colors @> '{0}'::integer[])
-> Bitmap Index Scan on items_fast_colors_rdtree2_idx
(cost=0.00..14.24 rows=251 width=0)
Index Cond: (fast_colors @> '{0}'::integer[])
(5 rows)

Any insight is greatly appreciated. Could this be a regression from
8.3.5 and 8.3.6?

Thanks,

Rusty
--
Rusty Conover
rconover(at)infogears(dot)com
InfoGears Inc / GearBuyer.com / FootwearBuyer.com
http://www.infogears.com
http://www.gearbuyer.com
http://www.footwearbuyer.com