MySQL Index Questions

myisamMySQL

I have 2 MyISAM tables:

table: search_hit with primary key: search_hit_id, and foreign key: search_id (150 million rows and growing with constant inserts)
table: search with primary key: search_id (about 30,000 rows and growing)

search_hit table has a number of indices,including search_id, but this query is excruciatingly slow:

select sq.search_id, count(ssh.search_hit_id)
from search sq
inner join search_hit ssh 
use index(by_search_id) on sq.search_id = ssh.search_id
where sq.search_id >= 47000
group by sq.search_id

here is the explain results:

1, 'SIMPLE', 'sq', 'range', 'PRIMARY', 'PRIMARY', '4', '', 202, 'Using where; Using index'
1, 'SIMPLE', 'ssh', 'ref', 'by_search_id', 'by_search_id', '4', 'lims.sq.search_id', 3358, ''

query returns with status like:
/* 0 rows affected, 1,575 rows found. Duration for 1 query: 3.198 sec. (+ 5.975 sec. network) */

Our server setup MySQL 5.0.45 on 64 bit linux with 8GB dual core (hyperthreaded quancore).
Would dropping the index, optimize table then re-create the index help here, or anything?

Thanks

David

Best Answer

You must refactor the query to perform WHERE, JOIN and GROUP BY clauses IN THAT EXACT ORDER !!!

Here is the refactored query :

select
    sq.search_id,
    count(1) search_id_count
from
    (select search_id from search where search_id > 47000) sq
    inner join
    (select search_id from search_hit where search_id > 47000) ssh
    using (search_id)
group by
    sq.search_id;

Running OPTIMIZE TABLE (reduces table fragmentation and recreate indexes) may not be necessary unless you do heavy INSERTs, UPDATEs, DELETEs. I'll say it is optional.

Give it a Try !!!

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