MySql 并发查询慢

Question

I'm running queries in parallel against a MySql database. Each query takes less than a second and another half a second to a second to fetch.

This is acceptable for me. But when I run 10 of these queries in parallel and then attempt another set in a different session everything slows down and a single query can take some 20 plus seconds.

My ORM is hibernate and I'm using C3P0 with <property name="hibernate.c3p0.max_size">20</property> . I'm sending the queries in parallel by using Java threads. But I don't think these are related because the slowdown also happens when I run queries in MySql Workbench . So I'm assuming something in my MySql config is missing, or the machine is not fast enough.

This is the query:

select 
    *
FROM
    schema.table
where
    site = 'sitename' and (description like '% family %' or title like '% family %')
limit 100 offset 0;

How can I make this go faster when facing let's say 100 concurrent queries?

Answer 1

I'm guessing that this is slow because the where clause is doing a full text search on the description and title columns; this will require the database to look through the entire field on every record, and that's never going to scale.

Each of those 10 concurrent queries must read the 1 million rows to fulfill the query. If you have a bottleneck anywhere in the system - disk i/o, memory, CPU - you may not hit that bottleneck with a single query, but you do hit it with 10 concurrent queries. You could use one of these tools to find out which bottleneck you're hitting.

Most of the time, those bottlenecks (CPU, memory, disk) are too expensive to upgrade - especially if you need to scale to 100 concurrent queries. So it's better to optimize the query/ORM approach.

I'd consider using Hibernate's built-in free text capability here - it requires some additional configuration, but works MUCH better when looking for arbitrary strings in a textual field.