When looking at queries that are candidates for optimization I often recommend that people look at rows_sent and rows_examined values as available in the slow query log (as well as some other places). If rows_examined is by far larger than rows_sent, say 100 larger, then the query is a great candidate for optimization. Optimization could be as simple as adding a few indexes or much more complicated as in generating summary tables so you do not need to rely on large aggregations for your real-time queries.

Just to be clear this is a great rule for your “real time” queries need to be handled very quickly and in high volumes. Batch jobs, reporting queries often will have to scan through millions of rows to get few rows of result set and it is fine.

So it is all clear with rows_sent being smaller than rows_examined but can it be smaller ? Yes it can! Here are couple …

The MySQL client has some functionalities some of us never use. Why would you use them and what is the added value of this?

Every DBA and developer has had a moment when he or she needs to connect to a MySQL database using the command line tool. Therefore I’ve written down an explanation of some command line commands you can insert in the CLI, most of them give added value and make your experience with the cli more enjoyable.

prompt

Who has never witnessed the scary feeling of not being connected to the write database when having several terminals open. I do, due to the fact I use the prompt functionality.

mysql >\R Production >
PROMPT set to 'Production > '

Or you can go a bit further and visualise the user, host and active database in:

mysql > \R \u@\h [\d]>
PROMPT set to '\u@\h [\d]>'
root@testbox [test]>

edit

In some …

In my previous post I pointed out that the existing ARCHIVE storage engine in MySQL may not be the one that will satisfy your needs when it comes to effectively storing large and/or old data. But are there any good alternatives? As the primary purpose of this engine is to store rarely accessed data in disk space efficient way, I will focus here on data compression abilities rather then on performance.

The InnoDB engine provides compressed row format, but is it’s efficiency even close to the one from that available in archive engine? You can also compress MyISAM tables by using myisampack tool, but that also means a table will be read only after such operation.

Moreover, I don’t trust MyISAM nor Archive when it comes to data durability. Fortunately along came a quite new (open source since April …

Next Wednesday, Severalnines CTO Johan Andersson and I will co-present a webinar about ClusterControl, a cluster management tool created by Severalnines that can monitor Percona XtraDB Cluster. It provides DBAs with the right metrics to manage and optimize applications during development and production.

In the webinar, titled “Performance Monitoring and Troubleshooting of Percona XtraDB Cluster,” we will discuss ClusterControl in general, and then we will explain how to install ClusterControl 1.2.5 in agentless mode. This is a particularly interesting use-case for me because in this …

A couple of weeks ago, shortly after Vadim wrote about Percona Cloud Tools and using Slow Query Log to capture the data, Mark Leith asked why don’t we just use Performance Schema instead? This is an interesting question and I think it deserves its own blog post to talk about.

First, I would say main reason for using Slow Query Log is compatibility. Basic Slow query log with microsecond query time precision is available starting in MySQL 5.1, while events_statements_summary_by_digest table was only added in MySQL 5.6 which was out for …

Next week (Wednesday, February 12 at 10 a.m. Pacific) I will host a webinar titled “Analyze MySQL Query Performance with Percona Cloud Tools.” Percona Cloud Tools, currently in beta, reveals new insights about MySQL performance enabling you to improve your database queries and applications. (You can request access to the free beta here).

For webinar attendees, Percona will raffle five (5) 60-minute MySQL query consulting sessions with me to analyze your Percona Cloud Tools query data and provide feedback and performance suggestions. Read below for how to win.

In the webinar I will cover:

• Setting up Percona Cloud Tools Query Analytics
• Deciphering advanced …

Here in Percona Support, we’re receiving several requests per day for help with Percona Cloud Tools installation steps.

So I decided to prepare a step-by-step example of the installation process with some comments based on experience.  Percona Cloud Tools is a hosted service providing access to query performance insights for all MySQL uses. After a brief setup, you’ll unlock new information about your database and how to improve your applications. You can sign up here to request access to the free beta, currently under way.

Some notes

• It’s recommended to do the installation under root.
• If you’re installing pt-agent as root then .pt-agent.conf should be placed in root $HOME
• You could became root …

This is the first in a series of posts highlighting a few of the seldom-used but still handy Percona Toolkit tools.

Have you ever had a problem understanding the EXPLAIN statement output? And are you the type of person who would rather use the command line than a GUI application? Then I would recommend that you use Percona’s pt-visual-explain toolkit. This is one of many Percona Toolkit tools that is useful for those who want to have a different view and an easier time understanding the EXPLAIN output aside from the usual table and vertical views.

As described in the documentation – http://www.percona.com/doc/percona-toolkit/2.2/pt-visual-explain.html#description

“pt-visual-explain reverse-engineers …

When we are hired for a MySQL performance audit, we are expected to review the MySQL configuration and to suggest improvements. Many people are surprised because in most cases, we only suggest to change a few settings even though hundreds of options are available. The goal of this post is to give you a list of some of the most critical settings.

We already made such suggestions in the past here on this blog a few years ago, but things have changed a lot in the MySQL world since then!

Before we start…

Even experienced people can make mistakes that can cause a lot of trouble. So before blindly applying the recommendations of this post, please keep in mind the following items:

• Change one setting at a time! This is the only way to estimate if a change is beneficial.
• Most …

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 killed MySQL server due to high Memory usage… OR with a question like: “I don’t know why mysql is taking so much memory. How do I find where exactly memory is allocated? please help!”

There are many ways to check memory consumption of MySQL. So, I’m just trying here to explain it by combining all details that I know of in this post.

• Check memory related Global/Session variables.

If you are using …