Proper full text index Rails/PostgreSQL/pg_search

问题:

I am testing performance for PostgreSQL full text search (using pg_search gem) and solr (sunspot_solr gem).

For 4 million records I am getting 13456 ms for Tsearch and 800 ms with SOLR (that is SOLR query + DB retrival). It is obvious that I need index but I am not sure how to create one for full text search. I investigated and found that for full text search I should use GIN index.

execute "CREATE INDEX products_gin_title ON products USING GIN(to_tsvector('english', title))"

But I am searching via two more columns and I need multi-value index and I am not sure how to implement it? I am not very familiar with DB part. My search code looks like:

@results = Product.search_title(params[:search_term]).where("platform_id=? AND product_type=?", params[:platform_id], params[:type_id]).limit(10).all

How do I create proper query for this type of situations?

Here is SQL output from rails for search term car.

Product Load (12494.0ms)
SELECT 
    "products".*, 
    ( ts_rank((to_tsvector('simple', coalesce("products"."title"::text, ''))), (to_ tsquery('simple', ''' ' || 'car' || ' ''')), 2) ) AS pg_search_rank 
FROM "products" 
WHERE (((to_tsvector('simple', coalesce("products"."tit le"::text, ''))) @@ (to_tsquery('simple', ''' ' || 'car' || ' ''')))) 
    AND (platform_id='26' AND product_type='2') 
ORDER BY pg_search_rank DESC, "products"."id" ASC 
LIMIT 10

EDIT:

I am using PostgreSQL 8.4.11, EXPLAIN ANALYZE output is following.

Limit  (cost=108126.34..108126.36 rows=10 width=3824) (actual time=12228.736..12228.738 rows=10 loops=1)   
->  Sort (cost=108126.34..108163.84 rows=14999 width=3824) (actual time=12228.733..12228.734 rows=10 loops=1)
    Sort Key: (ts_rank(to_tsvector('simple'::regconfig, COALESCE((title)::text, ''::text)), '''car'''::tsquery, 2)), id
    Sort Method:  top-N heapsort  Memory: 18kB
    ->  Seq Scan on products  (cost=0.00..107802.22 rows=14999 width=3824) (actual time=7.532..12224.585 rows=977 loops=1)
        Filter: ((platform_id = 26) AND (product_type = 2) AND (to_tsvector('simple'::regconfig, COALESCE((title)::text, ''::text)) @@ '''car'''::tsquery)) 

Total runtime: 12228.813 ms

回答1:

This expression:

to_tsvector('simple', (COALESCE(title::TEXT), ''))

is not sargable against your index.

You should declare the index on the exactly that expression which is used in the query:

CREATE INDEX products_gin_title
ON products
USING GIN(to_tsvector('simple', COALESCE(title::TEXT,'')))

(or make ruby generate the expression which is used in the index).

If you want multiple columns to be indexed, just concatenate them:

CREATE INDEX products_gin_title
ON products
USING GIN(to_tsvector('simple', title || ' ' || product_type || ' ' || platform_id))

but again, Ruby should be filtering on exactly same expression for the index to be of use.