Recently I was dealing with an unexpected issue raised by our Support customer, in which data became inconsistent after a schema change was applied.

After some investigation, it turned out that affected tables had a special word in the comments of some columns, which triggered an already known (and fixed) issue with the TableParser.pm library of Percona Toolkit.  The problem is that the customer was using an outdated Toolkit version, where pt-online-schema-change was using that buggy parser.

This bug applies only to Percona Toolkit versions up to 3.0.10, so if you have already 3.0.11 or newer installed, you can skip the rest of this post as these are no longer affected.

I am writing this post to warn every user of pt-online-schema-change who has not upgraded the toolkit, as …

Visibility is a blessing, and with databases, visibility is a must. That’s true not only for metrics but for the queries themselves. Having info on all the stats around query execution is priceless, and Percona Monitoring and Management (PMM) offers that in the form of the Query Analytics dashboard (QAN).

But where to start? QAN helps you with that by calculating the query profile. What is the profile? It’s a rank of queries, ordered by Load, so it is easy to spot the heaviest queries hitting your database. The Load is defined as the “Average Active Queries” but can also be defined as a mix of Query Execution Time Plus Query count. In other words, all the time the query was alive and kicking.

The Profile in PMM 2.10.0 looks like this:

The purpose of this profile is to facilitate the task of finding the …

Schema changes are the big challenges in Galera replication. So, it is recommended to understand the schema changes operation for everyone who uses the Percona XtraDB Cluster (PXB)/Galera clusters. In this blog, I am going to explain the operation and impact of the various schema changes methods used in the PXB/Galera cluster.

• Schema changes with “wsrep_OSU_method = TOI”
• Schema changes with “wsrep_OSU_method = RSU”
• Schema changes with “ONLINE ALGORITHMS”
• Schema changes with “pt-osc”
• Schema changes with “gh-ost”

For testing:

• I have configured the 3-node Percona Xtradb Cluster (8.0.19).
• Executing read/write load using the sysbench.

mysql> select @@wsrep_cluster_address\G
*************************** 1. row …

We all like when error messages are descriptive and give a clear idea about what is happening; however, there are some cases when a few possible reasons lay behind one error message. “MySQL server has gone away” is one of them. Most of the cases when the error occurs are described in MySQL documentation, but it can get tricky. And here, I’d like to talk about “tricky”.

There are only a few major cases when this happens:

1. MySQL Thread Was Killed by an Administrator or a Utility Such as pt-kill

The manual intervention is likely to be intermittent and, as it is a one-time thing in certain situations (e.g., a bad long-running query), probably would be known to a DBA. Pt-kill might be less noticeable, as it is often left running as a workaround to prevent those bad long queries from taxing system resources. Checking the system …

MySQL 8.0 General Availability release was launched in April 2018, and since then there have been ten versions of MySQL 8 and Percona Server for MySQL released. The MySQL Community expressed a high opinion of the MySQL 8.0 advantages, so a lot of databases have been successfully upgraded to the new version. But many of them still need to be up to date.

Percona has prepared a free course “How to Upgrade to MySQL 8.0” that helps you with this task.

It is a series of useful videos for 3-4 minutes. At the end of the course, you can pass the QUIZ and get a certificate. 

Follow the link to take the course:  https://classroom.google.com/c/MTM2MDIyNDIzMDQy?cjc=zjsst4l

You can also join the course manually. Just open Google Classroom and click “Join class” and enter the code of the class “zjsst4l”. …

One of the questions you often will be faced with operating a Linux-based system is managing memory budget. If a program uses more memory than available you may get swapping to happen, oftentimes with a terrible performance impact, or have Out of Memory (OOM) Killer activated, killing process altogether.

Before adjusting memory usage, either by configuration, optimization, or just managing the load, it helps to know how much memory a given program really uses.

If your system runs essentially a single user program (there is always a bunch of system processes) it is easy.  For example, if I run a dedicated MySQL server on a system with 128GB of RAM I can use “used” as a good proxy of what is used and “available” as what can still be used.

root@rocky:/mnt/data2/mysql# free -h …

InnoDB ReplicaSet was introduced from MySQL 8.0.19. It works based on the MySQL asynchronous replication. Generally, InnoDB ReplicaSet does not provide high availability on its own like InnoDB Cluster, because with InnoDB ReplicaSet we need to perform the manual failover. AdminAPI includes the support for the InnoDB ReplicaSet. We can operate the InnoDB ReplicaSet using the MySQL shell. 

• InnoDB cluster is the combination of MySQL shell and Group replication and MySQL router
• InnoDB ReplicaSet is the combination of MySQL shell and MySQL traditional async replication and MySQL router

Why InnoDB ReplicaSet?

• You can manually perform the switchover and failover with InnoDB ReplicaSet
• You can easily add the new node to your replication environment. InnoDB ReplicaSet helps with data provisioning (using MySQL clone plugin) and setting up the replication.

In this …

Have you ever had to provision a large number of instances from a single backup? The most common use case is having to move to new hardware, but there are other scenarios as well. This kind of procedure can involve multiple backup/restore operations which can easily become a pain to administer. Let’s look at a potential way to make it easier using Percona Xtrabackup. The Percona XtraBackup tool provides a method of performing fast and reliable backups of your MySQL data while the system is running.

Leveraging Named Pipes

As per the Linux manual page, a FIFO special file (a named pipe) is similar to a pipe except that it is accessed as part of the filesystem. It can be opened by multiple processes for reading or writing.

For this …

We are excited to let you know about two upcoming changes to Percona XtraBackup which will align Percona XtraBackup Versions with Percona Server for MySQL.  These changes are to bring Percona XtraBackup release naming line with Percona Server and MySQL and ensure Percona XtraBackup executes complete backups.

The first is a change to the naming structure of releases.  This change is something we believe will help when working with Percona products and is designed to position Percona XtraBackup to be in sync with the current release naming strategy of Percona Server for MySQL and Percona XtraDB Cluster.

The current naming structure of …

Disclaimer: the following script only works for Percona Server for MySQL 5.7, and relies on enabling performance schema (PS) instrumentation which can add overhead on high concurrent systems, and is not intended for continuous production usage as it’s a POC (proof of concept).

Introduction

In Percona Support, we frequently receive tickets related to deadlocks and even though the deadlock concept is simple, troubleshooting might not be in all cases. 

As explained in How to Deal with MySQL Deadlocks, a deadlock occurs when two or more transactions mutually hold and request for locks, creating a cycle of dependencies. MySQL will detect deadlocks and kill one of the transactions (making it rollback), and the deadlock will be printed in SEIS (show engine innodb status). Limitations of using this approach …