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How to Find MySQL Slow Queries in a Production Server by Activating the Slow Query Log - 2 minutes - Lately in PHP Podcast Episode 93 Part 2

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Updated on: 2022-10-19

Posted on: 2022-10-19

Viewers: 217 (October 2022)

Categories: PHP Tutorials, Lately in PHP Podcast

When you want to optimize a MySQL database application in production, you should figure out the slowest queries in that environment.

Enabling the MySQL slow query log can help you figure out the slowest SQL queries to optimize first. You can do that in a production environment, but you need to take extra care with how you enable the slow query log to avoid causing harm to the application.

Read this article, watch a 2-minute video, or listen to part 2 of episode 93 of the Lately in PHP podcast to learn how to enable the MySQL slow query log in a production environment in a safe way.




Loaded Article

In this article you can learn:

How to Improve the Speed of An Application that Uses a MySQL Database Server

1. Previous Article: Find MySQL Slow Queries by Activating the Slow Query Log

3. Next Article: Find How to Discover Which Are the Slowest Queries


Contents


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Episode 93 Part 1 Video

What was said in the podcast

Find MySQL Slow Queries by Activating the Slow Query Log in a Production Server

1. How to Find the Path of the Slow Query Log in a Production Server

There is an alternative way to show the slow query log file path. This is important because you need to monitor that file to look for queries that may be slow.

You can use this even in a production system. So if you have a real an application running, it's already in production, you can do this in your production environment. There is an alternative way to show the slow query log file path.

mlemos@development:~> mysql -u root -p -e "SHOW GLOBAL VARIABLES LIKE 'slow_query_log_file';"
Enter password: 
+---------------------+--------------------------------+
| Variable_name       | Value                          |
+---------------------+--------------------------------+
| slow_query_log_file | /var/log/mysql/mysqld_slow.log |
+---------------------+--------------------------------+
mlemos@development:~> 

This is important because you need to monitor that file to look up for queries that may be slow. You can use this even in a production system. So if you have a real application running, it's already in production, you can do this in your production environment.

2. How to Restart a MySQL Server to Update the Slow Query Log in Secure Way

Just be careful because you only restart the database server. You may halt some process that is running. So just be careful and do not restart the server when there are some queries being executed that are important.

So what I advise is that you pause your application somehow. Enable an option that no queries will be executed during the update.

So once you change the database options and restart the server you can resume the application. It's normal to have a maintenance mode that will help you to do these changes in a smooth way.

So let's move on to the next step.

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