Re: Slow search.. quite clueless

On 9/20/05, Yonatan Ben-Nes <da(at)canaan(dot)co(dot)il> wrote:
>
> Hi all,
>
> Im building a site where the users can search for products with up to 4
> diffrent keywords which all MUST match to each product which found as a
> result to the search.
>
> I got 2 tables (which are relevant to the issue :)), one is the product
> table (5 million rows) and the other is the keyword table which hold the
> keywords of each product (60 million rows).
>
> The scheme of the tables is as follows:
>
> Table "public.product"
> Column | Type | Modifiers
> ----------------------------+---------------+---------------------
> product_id | text | not null
> product_name | text | not null
> retail_price | numeric(10,2) | not null
> etc...
> Indexes:
> "product_product_id_key" UNIQUE, btree (product_id)
>
> Table "public.keyword"
> Column | Type | Modifiers
> -------------+---------------+-----------
> product_id | text | not null
> keyword | text | not null
> Indexes:
> "keyword_keyword" btree (keyword)
>
> The best query which I succeded to do till now is adding the keyword
> table for each keyword searched for example if someone search for "belt"
> & "black" & "pants" it will create the following query:
>
> poweraise.com=# EXPLAIN ANALYZE SELECT
>
> product_id,product_name,product_image_url,short_product_description,long_product_description,discount,discount_type,sale_price,retail_price
> FROM product INNER JOIN keyword t1 USING(product_id) INNER JOIN keyword
> t2 USING(product_id) INNER JOIN keyword t3 USING(product_id) WHERE
> t1.keyword='belt' AND t2.keyword='black' AND t3.keyword='pants' LIMIT 13;
>
> QUERY PLAN
>
> -----------------------------------------------------------------------------------------------------------------------------------------------------------------------
> Limit (cost=37734.15..39957.20 rows=13 width=578) (actual
> time=969.798..1520.354 rows=6 loops=1)
> -> Hash Join (cost=37734.15..3754162.82 rows=21733 width=578)
> (actual time=969.794..1520.337 rows=6 loops=1)
> Hash Cond: ("outer".product_id = "inner".product_id)
> -> Nested Loop (cost=18867.07..2858707.34 rows=55309
> width=612) (actual time=82.266..1474.018 rows=156 loops=1)
> -> Hash Join (cost=18867.07..2581181.09 rows=55309
> width=34) (actual time=82.170..1462.104 rows=156 loops=1)
> Hash Cond: ("outer".product_id = "inner".product_id)
> -> Index Scan using keyword_keyword on keyword t2
> (cost=0.00..331244.43 rows=140771 width=17) (actual
> time=0.033..1307.167 rows=109007 loops=1)
> Index Cond: (keyword = 'black'::text)
> -> Hash (cost=18851.23..18851.23 rows=6337
> width=17) (actual time=16.145..16.145 rows=0 loops=1)
> -> Index Scan using keyword_keyword on
> keyword t1 (cost=0.00..18851.23 rows=6337 width=17) (actual
> time=0.067..11.050 rows=3294 loops=1)
> Index Cond: (keyword = 'belt'::text)
> -> Index Scan using product_product_id_key on product
> (cost=0.00..5.01 rows=1 width=578) (actual time=0.058..0.060 rows=1
> loops=156)
> Index Cond: (product.product_id = "outer".product_id)
> -> Hash (cost=18851.23..18851.23 rows=6337 width=17) (actual
> time=42.863..42.863 rows=0 loops=1)
> -> Index Scan using keyword_keyword on keyword t3
> (cost=0.00..18851.23 rows=6337 width=17) (actual time=0.073..36.120
> rows=3932 loops=1)
> Index Cond: (keyword = 'pants'::text)
> Total runtime: 1521.441 ms
> (17 rows)
>
> Sometimes the query work fast even for 3 keywords but that doesnt help
> me if at other times it take ages....

Hmm, JOIN on a Huge table with LIMIT. You may be suffering from
the same problem I had:

http://archives.postgresql.org/pgsql-performance/2005-07/msg00345.php

Tom came up with a patch which worked marvellous in my case:

http://archives.postgresql.org/pgsql-performance/2005-07/msg00352.php

Try applying this patch, it may solve your problem!

Regards,
Dawid