Re: Slow search.. quite clueless

Oleg Bartunov wrote:
> contrib/tsearch2 (
> http://www.sai.msu.su/~megera/postgres/gist/tsearch/V2/ )
> might works for you. It might because performance depends on cardinality
> of your keywords.
>
> Oleg
> On Tue, 20 Sep 2005, Yonatan Ben-Nes 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....
>>
>> Now to find a result for 1 keyword its really flying so I also tried
>> to make 3 queries and do INTERSECT between them but it was found out
>> to be extremly slow...
>>
>> Whats make this query slow as far as I understand is all the merging
>> between the results of each table... I tried to divide the keyword
>> table into lots of keywords table which each hold keywords which start
>> only with a specific letter, it did improve the speeds but not in a
>> real significant way.. tried clusters,indexes,SET STATISTICS,WITHOUT
>> OIDS on the keyword table and what not.. im quite clueless...
>>
>> Actually I even started to look on other solutions and maybe you can
>> say something about them also.. maybe they can help me:
>> 1. Omega (From the Xapian project) - http://www.xapian.org/
>> 2. mnoGoSearch - http://www.mnogosearch.org/doc.html
>> 3. Swish-e - http://swish-e.org/index.html
>>
>> To add on everything I want at the end to be able to ORDER BY the
>> results like order the product by price, but im less concerned about
>> that cause I saw that with cluster I can do it without any extra
>> overhead.
>>
>> Thanks alot in advance,
>> Yonatan Ben-Nes
>>
>>
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>
> Regards,
> Oleg
> _____________________________________________________________
> Oleg Bartunov, sci.researcher, hostmaster of AstroNet,
> Sternberg Astronomical Institute, Moscow University (Russia)
> Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
> phone: +007(095)939-16-83, +007(095)939-23-83
>
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> match

Hi again everyone,

Oleg I tried tsearch2 and happily it does work wonderfully for me
returning results extremly fast and actually its working even better
then I wanted with all of those neat features like: lexem, weight & stop
words.

I got only one problem which is when I want the results to be ordered by
a diffrent field (like print INT field) it takes quite alot of time for
it to do it if the query can return lots of results (for example search
for the word "computer") and thats even if I limit the results.
The best way to improve its speed for such quereies (that I've found...)
is to create an index on the field which I want to order by and using it
CLUSTER the table, after the clustering I drop the the index so it won't
be used when I run queries with ORDER BY on that field, that seem to
improve the speed, if anyone got a better idea ill be glad to hear it.

Anyway thanks alot everyone!
Ben-Nes Yonatan