In the documentation and past messages to this list, it sounds like the btree_gist and btree_gin modules included in contrib/ in 8.4 should give me the functionality I'm looking for, but I don't seem to be getting the behavior I want.
I've made an example table representing something like a simplified version of a web discussion board.
Table "public.example" Column | Type | Modifiers ---------+----------+----------- body | text | vectors | tsvector | user_id | bigint |
I've got btree_gin and btree_gist installed, so I can make a composite index on vectors and user_id (which is a bigint).
create index index_examples_gin on example using gist (user_id,vectors); create index index_examples_gist on example using gist (user_id,vectors);
So what I'm expecting here is that it'll be able to use one of those composite indexes to satisfy both the user_id and the vectors constraints. That doesn't seem to be the case, based on this query plan:
explain analyze select body from example where user_id=1 and vectors @@ to_tsquery('simple', 'when') limit 10; QUERY PLAN ------------------------------------------------------------------------------------------------------------------------------------------------- Limit (cost=1786.87..10510.47 rows=10 width=5) (actual time=203.155..244.987 rows=10 loops=1) -> Bitmap Heap Scan on example (cost=1786.87..38425.99 rows=42 width=5) (actual time=203.153..244.980 rows=10 loops=1) Recheck Cond: (vectors @@ '''when'''::tsquery) Filter: (user_id = 1) -> Bitmap Index Scan on index_examples_gist (cost=0.00..1786.86 rows=26535 width=0) (actual time=186.711..186.711 rows=27477 loops=1) Index Cond: (vectors @@ '''when'''::tsquery) Total runtime: 245.062 ms (7 rows)
So it seems to be using the index only to satisfy the tsquery part of the where clause, and then applying the user_id filter to the rows it fetches. Ideally, I'd want to see it using both columns as part of the index condition, and not using a filter at all. Is what I'm trying to achieve possible?