October 23, 2014

Enum Fields VS Varchar VS Int + Joined table: What is Faster?

Really often in customers’ application we can see a huge tables with varchar/char fields, with small sets of possible values. These are “state”, “gender”, “status”, “weapon_type”, etc, etc. Frequently we suggest to change such fields to use ENUM column type, but is it really necessary (from performance standpoint)? In this post I’d like to present […]

Optimizing repeated subexpressions in MySQL

How smart is the MySQL optimizer? If it sees an expression repeated many times, does it realize they’re all the same and not calculate the result for each of them? I had a specific case where I needed to find out for sure, so I made a little benchmark. The query looks something like this:

How expensive is a WHERE clause in MySQL?

This is a fun question I’ve been wanting to test for some time.  How much overhead does a trivial WHERE clause add to a MySQL query?  To find out, I set my InnoDB buffer pool to 256MB and created a table that’s large enough to test, but small enough to fit wholly in memory:

Query Profiling with MySQL: Bypassing caches

Quite frequently I run into question like this “I’m using SQL_NO_CACHE but my query is still much faster second time I run it, why is that ? The answer to this question is simple – because SQL_NO_CACHE only bypasses query cache but it has no change on other caches, which are MySQL Caches – Innodb […]

To SQL_CALC_FOUND_ROWS or not to SQL_CALC_FOUND_ROWS?

When we optimize clients’ SQL queries I pretty often see a queries with SQL_CALC_FOUND_ROWS option used. Many people think, that it is faster to use this option than run two separate queries: one – to get a result set, another – to count total number of rows. In this post I’ll try to check, is […]

Getting real life query speeds with MySQL

To check for query performance improvements followed indexing/query changes or MySQL configuration changes our customers often decide to run the query and see if there is any significant improvement. Leaving aside question of checking single query alone might not be the best way to see real improvement for your application, the problem they usually run […]

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 […]

Cache Performance Comparison

Jay Pipes continues cache experiements and has compared performance of MySQL Query Cache and File Cache. Jay uses Apache Benchmark to compare full full stack, cached or not which is realistic but could draw missleading picture as contribution of different components may be different depending on your unique applications. For example for application containing a […]

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 […]

Are larger buffers always better ?

Sometimes I see people thinking about buffers as “larger is always better” so if “large” MySQL sample configuration is designed for 2GB and they happen to have 16, they would simply multiply all/most values by 10 and hope it will work well. Obviously it does not. The least problem would be wasting memory, allocating a […]