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Displaying posts with tag: MySQL (reset)
Using MySQL Offline Mode To Disconnect All Client Connections

As a DBA, one of the very frequent tasks is to stop/start MySQL service for batching or some other activities. Before stopping MySQL, we may need to check if there are any active connections; if there are, we may need to kill all those. Generally, we use pt-kill to kill the application connections or prepare kill statements using the select queries.

Example commands:

pt-kill --host= --user=percona -p --sentinel /tmp/pt-kill.sentinel2 --pid /tmp/  --victims all --match-command 'Query' --ignore-user 'pmm|rdsadmin|system_user|percona' --busy-time 10 --verbose --print --kill 

select concat('kill ',id,';') from information_schema.processlist where user='app_user';

MySQL has a variable called offline_mode to set the server into maintenance mode. When you set this, it immediately disconnects all the client connections that don’t …

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How to copy a MySQL instance ?

To copy a MySQL server to another server or to the cloud, there are several ways.

We can distinguish between two different types of copy:

  • physical copy
  • logical copy

The physical copy is often the fastest. However, it requires some tools to ensure that you have a consistent online backup. For example, you can use MySQL Enterprise Backup (MEB).

Alternatively, it’s possible to use the CLONE plug-in to provision a new instance with existing data from a source server. This is my preferred approach.

Finally, the last physical solution is the use of a file system snapshot, but this requires the right infrastructure and even more care to have a consistent …

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Don’t Start Using Your MySQL Server Until You’ve Configured Your OS

Whenever you install your favorite MySQL server on a freshly created Ubuntu instance, you start by updating the configuration for MySQL, such as configuring buffer pool, changing the default datadir director, and disabling one of the most outstanding features – query cache. It’s a nice thing to do, but first things first. Let’s review the best practices we usually follow in Managed Services before using your MySQL server in production and stage env, even for home play purposes.


Our usual recommendation is to use specific memory parameters, which we suggest to ensure optimal performance.

  • To prevent out-of-memory (OOM) episodes, the OOM Score has to be set to -800.
  • vm.swappiness = 1
  • Disable Transparent Huge Pages
  • Install and enable jemalloc. Let’s briefly go through each setting to understand why adjustments are needed. Afterward, we will see how to configure these …
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Developer Interview with Wendell Adriel – OpenLampTech Repost

OpenLampTech continues to publish great content for the PHP, MySQL, LAMP stack, and open-source communities. This week, I (am resharing) have another awesome text-based developer interview for you with Wendell Adriel. Thanks for reading!

The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

Visit and read Wendell’s fantastic interview here:

If you’re not already …

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The MySQL Clone Plugin Is Not Your Backup

This blog post discusses the limitations of the MySQL Clone plugin.

The MySQL clone plugin significantly simplifies the process of replica provisioning. All you need to do is:

  • Ensure that the source server has binary logs enabled
  • Grant appropriate permissions
  • Execute the CLONE INSTANCE  command on the recipient

This works extremely easily when you provision a new replica that doesn’t have any data.

Due to its simplicity, you may want to use the clone plugin instead of a backup to restore a server that survives data inconsistency or corruption. E.g., after crash.

However, if you have data on your replica, you need to consider how you will recover if the CLONE INSTANCE  command fails with an error.

CLONE INSTANCE  command, by default, works as follows:

  • Checks prerequisites on the replica
  • Wipes out data …
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Explore the New Feature of MySQL To Restrict Users From Creating a Table Without a Primary Key

As MySQL database administrators, we are well aware of the significance of implementing a primary key within a table. Throughout our careers, most of us have encountered situations where the absence of a primary key has led to operational challenges. Primary keys play an indispensable role in sound database design by uniquely identifying individual rows and significantly enhancing data retrieval, manipulation, and overall system performance.

From the MySQL documentation:

The PRIMARY KEY clause is a critical factor affecting the performance of MySQL queries and the space usage for tables and indexes. The primary key uniquely identifies a row in a table. Every row in the table should have a primary key value, and no two rows can have the same primary key value.

It is common for tables to be inadvertently created without a primary key, often leading to regrettable consequences that we only recognize when issues …

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Restrict MySQL Connections to Broken Replica in ProxySQL

ProxySQL is a high-performance SQL proxy, which runs as a daemon watched by a monitoring process. The process monitors the daemon and restarts it in case of a crash to minimize downtime.

The daemon accepts incoming traffic from MySQL clients and forwards it to backend MySQL servers.

The proxy is designed to run continuously without needing to be restarted. Most configurations can be done at runtime using queries similar to SQL statements in the ProxySQL admin interface. These include runtime parameters, server grouping, and traffic-related settings.

Here, we will consider ProxySQL configured for async replication. Even when a replica is broken/stopped, ProxySQL still routes connections to replicas. It can be overcome by setting the appropriate value for mysql-monitor_slave_lag_when_null

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Quick Look – MySQL Data Directory Files

Do you know what lies inside your MySQL Data Directory? This article is a quick guide about the files stored inside MySQL data directory. Data managed by the MySQL server…

The post Quick Look – MySQL Data Directory Files first appeared on Change Is Inevitable.

OpenLampTech issue #97 – Newsletter Repost

Another packed full newsletter coming your way this week in OpenLampTech. So much goodness in this one. Take your time reading, enjoy, and share. Thank you.

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The Newsletter for PHP and MySQL Developers

Receive a copy of my ebook, “10 MySQL Tips For Everyone”, absolutely free when you subscribe to the OpenLampTech newsletter.

In OpenLampTech issue #97, there is great content on:

  • Developer interview
  • MySQL …
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Cut & Paste a User Creation Statement with MySQL 8

Sometimes it’s convenient to retrieve the user creation statement and to copy it to another server.

However, with the new authentication method used as default since MySQL 8.0, caching_sha2_password, this can become a nightmare as the output is binary and some bytes can be hidden or decoded differently depending of the terminal and font used.

Let’s have a look:

If we cut the create user statement and paste it into another server what will happen ?

We can see that we get the following error:

ERROR: 1827 (HY000): The password hash doesn't have the expected format.

How could we deal with that ?

The solution to be able to cut & paste the authentication string without having any issue, is to change it as a binary representation (hexadecimal) like this:

And then replace the value in the user create statement:

But there is an easier way. …

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