August 29, 2014

Working with large data sets in MySQL

What does working with large data sets in mySQL teach you ? Of course you have to learn a lot about query optimization, art of building summary tables and tricks of executing queries exactly as you want. I already wrote about development and configuration side of the problem so I will not go to details […]

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 […]

OOM relation to vm.swappiness=0 in new kernel

I have recently been involved in diagnosing the reasons behind OOM invocation that would kill the MySQL server process. Of course these servers were primarily running MySQL. As such the MySQL server process was the one with the largest amount of memory allocated. But the strange thing was that in all the cases, there was […]

utf8 data on latin1 tables: converting to utf8 without downtime or double encoding

Here’s a problem some or most of us have encountered. You have a latin1 table defined like below, and your application is storing utf8 data to the column on a latin1 connection. Obviously, double encoding occurs. Now your development team decided to use utf8 everywhere, but during the process you can only have as little […]

How to reclaim space in InnoDB when innodb_file_per_table is ON

When innodb_file_per_table is OFF and all data is going to be stored in ibdata files. If you drop some tables of delete some data then there is no any other way to reclaim that unused disk space except dump/reload method. When Innodb_file_per_table is ON, each table stores data and indexes in it’s own tablespace file. […]

Percona XtraDB Cluster 5.5.31-23.7.5 now available

Percona is glad to announce the release of Percona XtraDB Cluster 5.5.31-23.7.5 on June 25, 2013. Binaries are available from the downloads area or from our software repositories. New Features: Information about the wsrep sequence number has been added to INFORMATION_SCHEMA.INNODB_TRX table. Percona XtraDB Cluster can now be bootstrapped with the new bootstrap-pxc option in […]

Percona XtraDB Cluster (PXC) in the real world: Share your use cases!

The aim of this post is to enumerate real-world usage of Percona XtraDB Cluster (PXC), and also to solicit use cases from the readers. One of the prominent usages in the production environment that we have come across (and our Percona consultants have assisted) is that of HP Cloud. There is a post about it […]

Write contentions on the query cache

While doing a performance audit for a customer a few weeks ago, I tried to improve the response time of their top slow query according to pt-query-digest‘s report. This query was run very frequently and had very unstable performance: during the time data was collected, response time varied from 50µs to 1s. When I ran […]

Innodb Table Locks

Innodb uses row level locks right ? So if you see locked tables reported in SHOW ENGINE INNODB STATUS you might be confused and rightfully so as Innodb table locking is a bit more complicated than traditional MyISAM table locks. Let me start with some examples. First lets run SELECT Query:

As you can […]

How FLUSH TABLES WITH READ LOCK works with Innodb Tables

Many backup tools including Percona Xtrabackup, MyLVMBackup and others use FLUSH TABLES WITH READ LOCK to temporary make MySQL read only. In many cases the period for which server has to be made read only is very short, just few seconds, yet the impact of FLUSH TABLES WITH READ LOCK can be quite large because […]