April 19, 2014

MySQL Session variables and Hints

MySQL has two ways to find tune execution of particular query. First is MySQL Hints, such as SQL_BIG_RESULT, STRAIGHT_JOIN, FORCE INDEX etc. You place these directly into the query to change how query is executed for example SELECT STRAIGHT_JOIN * FROM A FORCE INDEX(A) JOIN B The other part is session variable. If you know […]

Can we improve MySQL variable handling ?

MySQL Settings (also known as Server Variables) have interesting property. When you set variable in running server this change is not persisted in any way and server will be back to old value upon restart. MySQL also does not have option to re-read config file without restarting as some other software so approach to change […]

Ultimate MySQL variable and status reference list

I am constantly referring to the amazing MySQL manual, especially the option and variable reference table. But just as frequently, I want to look up blog posts on variables, or look for content in the Percona documentation or forums. So I present to you what is now my newest Firefox toolbar bookmark: an option and […]

PHP Sessions – Files vs Database Based

One may think changing PHP session handler from file based to database driven is fully transparent. In many cases it is, sometimes however it may cause some unexpected problems as happened to one of our customers. If you use file based sessions PHP will lock session file for whole script execution duration, which means all […]

Generating test data for MySQL tables

One of the common tasks requested by our support customers is to optimize slow queries. We normally ask for the table structure(s), the problematic query and sample data to be able to reproduce the problem and resolve it by modifying the query, table structure, or global/session variables. Sometimes, we are given access to the server […]

MySQL server memory usage troubleshooting tips

There are many blog posts already written on topics related to “MySQL server memory usage,” but nevertheless there are some who still get confused when troubleshooting issues associated with memory usage for MySQL. As a Percona support engineer, I’m seeing many issues regularly related to heavy server loads – OR OOM killer got invoked and […]

Percona Server 5.5.35-33.0 is now available

Percona is glad to announce the release of Percona Server 5.5.35-33.0 on December 20th, 2013 (Downloads are available here and from the Percona Software Repositories). Based on MySQL 5.5.35, including all the bug fixes in it, Percona Server 5.5.35-33.0 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release […]

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 […]

Investigating MySQL Replication Latency in Percona XtraDB Cluster

I was curious to check how Percona XtraDB Cluster behaves when it comes to MySQL replication latency — or better yet, call it data propagation latency. It was interesting to see whenever I can get stale data reads from other cluster nodes after write performed to some specific node. To test it I wrote quite a […]

Timezone and pt-table-checksum

I recently worked through an issue with a client trying to detect data drift across some servers that were located in different timezones.  Unfortunately, several of the tables had timestamp fields and were set to a default value of CURRENT_TIMESTAMP.  From the manual, here is how MySQL handles timezone locality with timestamp fields: Values for TIMESTAMP columns are […]