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Updated June 1, 2023.

Suboptimal MySQL ORDER BY implementation, especially together with MySQL LIMIT is often the cause of MySQL performance problems. Here is what you need to know about MySQL ORDER BY LIMIT optimization to avoid these problems.

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MySQL LIMIT clause

The MySQL LIMIT clause is a valuable tool for controlling the number of rows returned by a SELECT statement. By specifying the maximum number of rows to retrieve from the result set, it enables you to work with subsets of data, especially in situations involving large tables. This feature enhances query performance and optimizes resource usage by fetching only …

Introduction Although there is an SQL Standard, every relational database is ultimately unique, and you need to adjust your data access layer so that you get the most out of the relational database in use. In this article, we are going to see what you can do to boost up performance when using MySQL with … Continue reading 9 High-Performance Tips when using MySQL with JPA and Hibernate →

This is just a note to myself. I don’t do this often enough to remember the command, but whenever I’m searching for this, it takes half a minute to find it in MySQL manual, so hopefully this gets indexed better (in my memory as well as in Google).

Here’s the simple command to create a login path:

mysql_config_editor set --login-path=mysql1  --host=localhost \
   --port=3306 --socket=/path/to/socket --user=root --password

Obviously you can remove just about anything and only leave the essentials.

Once that’s done, accessing different MySQL instances is as simple as mysql --login-path=mysql1, which is especially useful if you’re accessing different servers from one machine, or if you’re running several MySQL instances on the same machine.

More information on login paths …

The freshly released MySQL 8.0 includes a data dictionary, which makes MySQL much more reliable. Thanks to this features, we don't have any '.frm' files, and querying the information_schema is 30x to 100x faster than previous versions.

One drawback of the implementation is that the data dictionary tables are hidden by design.

While the reason is fully understandable (they don't want to commit on an interface that may change in the future) many curious users are disappointed, because openness is the basis of good understanding and feedback.

The problem to access the dictionary tables can be split in three parts:

• Finding the list of tables; …

We work on data recoveries quite often. In many cases, we recover table structures from the .frm files because there was no backup available. There is already a great blog post by my colleague Miguel Ángel Nieto about how we can recover structures from .frm files using MySQL utilities.

This works pretty well and we prefer to run mysqlfrm with the “–server” option to get all possible information from a .frm file. However, this option expects that MySQL is up and running so that mysqlfrm can spawn a new MySQL instance, and run the structure recovery there.

Recently I came across a tool that makes this job easier. The name of tool is …

During the PerconaLive conference in Amsterdam, I attended a session where I heard a good piece of advice about using GTID. It amounts to: look at SHOW SLAVE STATUS output, and if you see more than one line in the Executed_Gtid_Set field, this tells you immediately if someone has written on a slave database.
This is good advice. Let's dissect it. Here is what a regular slave looks like, when nobody has messed up with it:

SHOW SLAVE STATUS\G
*************************** 1. row ***************************
 [...]
             Master_Server_Id: 1
                  Master_UUID: 00013454-1111-1111-1111-111111111111
             Master_Info_File: mysql.slave_master_info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more …

You’ve probably had some troubles with the shared InnoDB tablespace stored in the ibdata file. Especially when it has grown for some reasons and reached a critical size.

This behavior occurs in some cases, due to excessive rollback segments growth or during a migration from a unique shared tablespace to a file-per-table configuration for example.

In this post, I would like to explain how to shrink the ibdata file after an unwanted file growth in a file-per-table configuration.
Note that the process could be done without Trite but the tool avoids to write the script used to transport tables yourself.

Initial situation

Here is a sample of the InnoDB configuration:

innodb_data_file_path = ibdata1:100M:autoextend
innodb_file_per_table

And the status of your datafiles in the datadir directory:

drwx------ 2 mysql mysql 4,0K déc. 20 2012 …

August 25, 2014 By Severalnines

Are you going in production with Galera Cluster for MySQL? Here are 9 tips to consider before going live. These are applicable to all 3 Galera versions (Codership, Percona XtraDB Cluster and MariaDB Galera Cluster). 

1. Galera strengths and weaknesses

There are multiple types of replication and cluster technologies for MySQL, make sure you understand how Galera works so you set the right expectations. Applications that run on single instance MySQL might not work well on Galera, you might need to make some changes to the application or the workload might not be appropriate. We’d suggest you have a look at these resources: 

• Tutorial on …

On Wednesday I gave a presentation on “How to Avoid Even More Common (but Deadly) MySQL Development Mistakes” for Percona MySQL Webinars.  If you missed it, you can still register to view the recording and my slides.

Thanks to everyone who attended, and especially to folks who asked the great questions.  I answered as many as we had time for  during the session, but here are all the questions with my complete answers:

Q: Disk bandwidth also not infinite

Indeed, you’re right! …