August 22, 2014

Using UNION to implement loose index scan in MySQL

One little known fact about MySQL Indexing, however very important for successfull MySQL Performance Optimization is understanding when exactly MySQL is going to use index and how it is going to do them. So if you have table people with KEY(age,zip) and you will run query something like SELECT name FROM people WHERE age BETWEEN […]

MySQL Query Cache

MySQL has a great feature called “Query Cache” which is quite helpful for MySQL Performance optimization tasks but there are number of things you need to know. First let me clarify what MySQL Query Cache is – I’ve seen number of people being confused, thinking MySQL Query Cache is the same as Oracle Query Cache […]

Distributed Set Processing with Shard-Query

Can Shard-Query scale to 20 nodes? Peter asked this question in comments to to my previous Shard-Query benchmark. Actually he asked if it could scale to 50, but testing 20 was all I could due to to EC2 and time limits. I think the results at 20 nodes are very useful to understand the performance: […]

When the subselect runs faster

A few weeks ago, we had a query optimization request from one of our customer. The query was very simple like:

This column in the table is looks like this:

The table have 549252 rows and of course, there is an index on the col1. MySQL estimated the cardinality of that index as […]

How adding another table to JOIN can improve performance ?

JOINs are expensive and it most typical the fewer tables (for the same database) you join the better performance you will get. As for any rules there are however exceptions The one I’m speaking about comes from the issue with MySQL optimizer stopping using further index key parts as soon as there is a range […]