From: | Jordi <jmaillists(at)promani(dot)be> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Bitmap and-ing between btree and gin? |
Date: | 2016-02-04 11:15:02 |
Message-ID: | 56B332B6.1040109@promani.be |
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Lists: | pgsql-performance |
Hello all,
I've been trying to get a query use indexes and it has raised a doubt
whether pgsql supports bitmap and-ing between a multi-column btree index
and a gin index.
The idea is to do a full-text search on a tsvector that is indexed with
gin. Then there are typical extra filters like is_active that you would
put in a btree index. Instead of using OFFSET I use a > operation on the
id. Finally, to make sure the results listing always appear in the same
order, I do an ORDER BY the id of the row. So something like this:
CREATE INDEX idx_gin_page ON page USING gin(search_vector);
CREATE INDEX idx_btree_active_iddesc ON page USING btree(is_active, id DESC);
SELECT * FROM page WHERE (( (page.search_vector) @@ (plainto_tsquery('pg_catalog.english', 'myquery'))) AND page.is_active = 1 AND page.id > 100) ORDER BY page.id DESC LIMIT 100;
Some options I considered:
- One big multi-column index with the btree_gin module, but that didn't
work. I suppose it's because just like gin, it doesn't support sorting.
- Seperate indexes as above, but that didn't work. The planner would
always choose the btree index to do the is_active=1 and id>100 filter
and the sorting, and within those results do a manual filter on the
tsvector, being extremely slow.
BUT: when I remove the ORDER BY statement, the query runs really fast.
It uses the 2 indexes seperately and bitmap-ands them together,
resulting in a fast executing query.
So my question is whether there is something wrong with my query or
indexes, or does pgsql not support sorting and bitmap and-ing?
Thanks and have a nice day
Jordi
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