Improve my psql query performance

Question

I have a psql query that performs odd. I defined a GIN index on the 2 columns that I use now for search:

Indexes:
"pk_products" PRIMARY KEY, btree (id)
"fk_affiliate_affiliate_product_id" UNIQUE, btree (affiliate_id, affiliate_product_id)
"idx_products" btree (merchant_id)
"idx_products_affiliates" btree (affiliate_id)
"idx_products_brand_id" btree (brand_id)
"idx_products_ts" gin (to_tsvector('english'::regconfig, (COALESCE(title, ''::character varying)::text || ' '::text) || COALESCE(description, ''::text)))

If I search for a short word, like 4 characters I get a fast query:

EXPLAIN ANALYZE SELECT p.id, p.price, p.currency, p.images, p.merchant_id
FROM products AS p
WHERE deleted=false AND to_tsvector('english', p.title || coalesce(p.description, '')) @@ to_tsquery('blue:*')
LIMIT 30 OFFSET 0;

Result:

QUERY PLAN

 Limit  (cost=0.00..219.47 rows=30 width=49) (actual time=3.138..40.914 rows=30 loops=1)
     ->  Seq Scan on products p  (cost=0.00..41120.86 rows=5621 width=49) (actual time=2.740..40.478 rows=30 loops=1)
     Filter: ((NOT deleted) AND (to_tsvector('english'::regconfig, ((title)::text || COALESCE(description, ''::text))) @@ to_tsquery('blue:*'::text)))
     Rows Removed by Filter: 153
  Total runtime: 40.986 ms
  (5 rows)

If I use a longer word:

EXPLAIN ANALYZE SELECT p.id, p.price, p.currency, p.images, p.merchant_id
FROM products AS p
WHERE deleted=false AND to_tsvector('english', p.title || coalesce(p.description, '')) @@ to_tsquery('turquoise:*')
LIMIT 30 OFFSET 0;

The time is increased:

QUERY PLAN

 Limit  (cost=0.00..219.47 rows=30 width=49) (actual time=1.097..1579.187 rows=30 loops=1)
   ->  Seq Scan on products p  (cost=0.00..41120.86 rows=5621 width=49) (actual time=1.093..1579.129 rows=30 loops=1)
     Filter: ((NOT deleted) AND (to_tsvector('english'::regconfig, ((title)::text || COALESCE(description, ''::text))) @@ to_tsquery('turquoise:*'::text)))
     Rows Removed by Filter: 12697
 Total runtime: 1579.287 ms
 (5 rows)

And if I use "-" in the word the time to get the result is huge:

EXPLAIN ANALYZE SELECT p.id, p.price, p.currency, p.images, p.merchant_id
FROM products AS p
WHERE deleted=false AND to_tsvector('english', p.title || coalesce(p.description, '')) @@ to_tsquery('turquoise-blue:*')
LIMIT 30 OFFSET 0;

The result:

QUERY PLAN

 Limit  (cost=0.00..41120.86 rows=2 width=49) (actual time=31400.164..31400.164 rows=0 loops=1)
   ->  Seq Scan on products p  (cost=0.00..41120.86 rows=2 width=49) (actual time=31400.158..31400.158 rows=0 loops=1)
     Filter: ((NOT deleted) AND (to_tsvector('english'::regconfig, ((title)::text || COALESCE(description, ''::text))) @@ to_tsquery('turquoise-blue:*'::text)))
     Rows Removed by Filter: 281510
 Total runtime: 31400.247 ms
 (5 rows)

Any ideas are greatly appreciated! Thank you!

EDIT:

I think is related to the number of results, a query that has no results takes longer?

Answer 1

Found the problem.

Changed the index like this:

"idx_products_ts" gin (to_tsvector('english'::regconfig, title::text || description))

And now the querys are really fast!

EXPLAIN ANALYZE SELECT p.id, p.price, p.currency, p.images, p.merchant_id
FROM products AS p
WHERE deleted=false AND to_tsvector('english', p.title || p.description) @@ to_tsquery('blue:*')
LIMIT 30 OFFSET 0;

QUERY PLAN

Limit  (cost=103.64..183.47 rows=30 width=49) (actual time=15.588..15.644 rows=30 loops=1)
 ->  Bitmap Heap Scan on products p  (cost=103.64..15084.42 rows=5630 width=49) (actual time=15.586..15.633 rows=30 loops=1)
     Recheck Cond: (to_tsvector('english'::regconfig, ((title)::text || description)) @@ to_tsquery('blue:*'::text))
     Filter: (NOT deleted)
     ->  Bitmap Index Scan on idx_products_ts  (cost=0.00..102.23 rows=5630 width=0) (actual time=12.955..12.955 rows=26747 loops=1)
           Index Cond: (to_tsvector('english'::regconfig, ((title)::text || description)) @@ to_tsquery('blue:*'::text))
Total runtime: 15.714 ms
(7 rows)

AND:

EXPLAIN ANALYZE SELECT p.id, p.price, p.currency, p.images, p.merchant_id
FROM products AS p
WHERE deleted=false AND to_tsvector('english', p.title || p.description) @@ to_tsquery('turquoise-blue:*')
LIMIT 30 OFFSET 0;

QUERY PLAN

Limit  (cost=108.02..116.02 rows=2 width=49) (actual time=26.234..26.234 rows=0 loops=1)
  ->  Bitmap Heap Scan on products p  (cost=108.02..116.02 rows=2 width=49) (actual time=26.226..26.226 rows=0 loops=1)
     Recheck Cond: (to_tsvector('english'::regconfig, ((title)::text || description)) @@ to_tsquery('turquoise-blue:*'::text))
     Filter: (NOT deleted)
     ->  Bitmap Index Scan on idx_products_ts  (cost=0.00..108.02 rows=2 width=0) (actual time=26.209..26.209 rows=0 loops=1)
           Index Cond: (to_tsvector('english'::regconfig, ((title)::text || description)) @@ to_tsquery('turquoise-blue:*'::text))
Total runtime: 26.433 ms
(7 rows)

A huge improvement from Total runtime: 31400.247 ms to Total runtime: 26.433 ms.