High season is coming, how do you make sure that MySQL will handle the increased load? Stress tests could help with that, but it’s not a good idea to run them in a production environment. In this case Select_scan, Select_full_join and other MySQL counters could quickly give you an idea of how many queries are not performing well and could cause a performance degradation as the load goes up.

Select_scan from SHOW GLOBAL STATUS indicates how many full table scans were done since last MySQL restart. Scanning the entire table is a resource intensive operation. It also forces MySQL to store unnecessary data in the buffer pool, wasting memory and IO resources.

Full scan of a tiny table would be quite fast so missing indexes could stay invisible until the load rises or the dataset grows up. This could also be the case for developers who work with too small data sets on their dev boxes. To prevent performance issues all newly added …

Often enough I find MySQL benchmark results where the difference between results is 1% or even less and some conclusions are drawn. Now it is not that 1% is not important – especially when you’re developing the product you should care about those 1% improvements or regressions because they tend to add up. However with such a small difference it is very important to understand whenever this is for real or it is just the natural variance for your baseline test.

Take a look at this graph:
Click the image for a larger view)

This is the result for a simple in-memory, read-only “select by primary key” SysBench benchmark on dedicated physical hardware that is otherwise idle, simple 1 socket system. I tried to stabilize it as much as possible, for example …

There were two nasty MySQL replication bugs in two different 5.6 releases that would make it difficult to upgrade slaves to MySQL 5.6 while still connected to MySQL 5.5 master. The first of those bugs is MySQL bug 72610 which affects 5.6.19. Essentially this bug is triggered when the table structure on the slave is different from the table structure on the master which leads to unnecessarily large amount of RAM usage while replicating events that affect that table. The amount of RAM used would generally be more noticeable when the replicated transaction consists of thousands of RBR events. The most common way this affects how we upgrade a replication hierarchy, is when we have the master running MySQL 5.5 and the slave running MySQL 5.6 and we have transactions involving DATETIME column(s). Tables with DATETIME columns will have different underlying structure when created on MySQL 5.5 versus when created on MySQL 5.6. Ideally you would avoid creating …

There were two nasty MySQL replication bugs in two different 5.6 releases that would make it difficult to upgrade slaves to MySQL 5.6 while still connected to MySQL 5.5 master.

The first of those bugs is MySQL bug 72610 which affects 5.6.19. Essentially this bug is triggered when the table structure on the slave is different from the table structure on the master which leads to unnecessarily large amount of RAM usage while replicating events that affect that table. The amount of RAM used would generally be more noticeable when the replicated transaction consists of thousands of RBR events.

The most common way this affects how we upgrade a replication hierarchy, is when we have the master running MySQL 5.5 and the slave running MySQL 5.6 and we have transactions involving DATETIME column(s). Tables with DATETIME columns will have different …

With the query rewrite framework in the latest MySQL (Optimizer/InnoDB/Replication) labs release, you get the opportunity to author plugins that can rewrite queries. You can choose whether to rewrite the queries before and/or after parsing. Today I am going to walk you through how to write a pre-parse query rewrite plugin.

When would you want to use a pre-parse query rewrite plugin? The greatest benefit compared to post-parse rewrites — which I cover in a separate post — is the efficiency, especially the lack of overhead for those queries that are actually rewritten. Typical cases where you may want to write a pre-parse plugin are:

• When you want to remove certain specific clauses from queries. For example, perhaps you want to remove all ENGINE …

I log into a lot of different servers running MySQL and one of the first things I do is create a file in my home directory called ‘.my.cnf’ with my credentials to that local mysql instance:

[client]
user=root
password=secret

This means I don’t have to type my password in every time, nor am I tempted to include it on the command line with -p and get the dreaded (but completely accurate):

Warning: Using a password on the command line interface can be insecure.

MySQL 5.6 introduces a utility to make this easier and more secure. First, let’s start with a new mysqld instance with a blank root password and make it more secure:

[vagrant@localhost ~]$ mysqladmin -u root password
New password:secret
Confirm new password:secret
[vagrant@localhost ~]$ mysql -u root
ERROR 1045 (28000): Access denied for user …

I just pushed the new Java based iiBench for MySQL (and Percona Server and MariaDB), the code and documentation are available now in the iibench-mysql Github repo. Pull request are welcome!

The history of iiBench goes back to the early days of Tokutek. Since "indexed insertion" is a strength of Fractal Tree indexes, the first iiBench was created by Tokutek in C++ back in 2008. Mark Callaghan rewrote iiBench in Python, adding several features along the way. His version of iiBench is available in …

People using OpenStack Trove instances can hit a common issue in the MySQL world: how to perform schema change operations while minimizing the impact on the database server? Let’s explore the options that can allow online schema changes.

Summary

With MySQL 5.5, pt-online-schema-change from Percona Toolkit is your best option for large tables while regular ALTER TABLE statements are only acceptable for small tables. Also beware of metadata locks.

With MySQL 5.6, almost all types of schema changes can be done online. Metadata locks can also be an issue. pt-online-schema-change can still be worth using as it is also online on read replicas.

Regular ALTER TABLE with MySQL 5.5

If you are still using MySQL 5.5, almost all schema changes will require a table …

I'm happy to announce the release of mylvmbackup version 0.16. The source package is now available for download from http://lenzg.net/mylvmbackup/ and https://launchpad.net/mylvmbackup.

Installation packages for a number of platforms can be obtained from the openSUSE Build Service.

Version 0.16 adds support for sending out SNMP traps in case of backup successes or failures. I'd like to thank Alexandre Anriot for contributing this new feature and his patience with me.

Please see the ChangeLog and bzr …

Performance Schema (P_S) has been available since MySQL 5.5, more than 4 years ago. It is still difficult to see production servers with P_S enabled, even with MySQL 5.6 where the feature is enabled by default. There have been several complaints like the overhead, that the fix is a work in progress, and the ease of use. 52 tables to query and 31 configuration variables is enough to scare people.

There is a solution for the second problem, the usability. It’s name is “sys schema“. It is a collection of views, functions and procedures to make P_S more user friendly.

Installation

If you are a MySQL Workbench user the installation is pretty easy because sys schema is already included. You just need to install it. Click on “Performance – Performance Reports” and there you will find the “Install Helper” button that will install sys schema. …