There is a common pattern in life, you often discover or understand things by accident. Many scientific discoveries fit such a description. In our database world, I was looking to see how BLOB/TEXT columns are allocated using overlay pages and I stumbled upon something interesting and unexpected. Let me present to you my findings, along with my attempt at explaining what is happening.

InnoDB Tablespaces

The first oddity I found is a bunch of free pages in each tablespace it is skipping. Here’s an example from a simple table with only an integer primary key and a char(32) column:

root@LabPS8_1:~/1btr# innodb_space -f /var/lib/mysql/test/t1.ibd space-extents
start_page  page_used_bitmap
0               #####################################........................... <--- free pages
64              ################################################################
128 …

This blog post will show how to compile the Percona XtraBackup (PXB) tool for ARM. For this, we are going to use an AWS EC2 ARM instance with Ubuntu 20.04(Focal Fossa).

The motivation for this was born in my interest in the new generation of ARM processors and if this is a viable option for the future. Ideally, I do not recommend installing all the necessary packages to compile Xtrabackup in a production environment for security reasons. Still, you can have a “compiling” server for this purpose and then move the binaries around.

Machine Configuration

For this blog post, I picked a c6g.2xlarge instance. The machine has the following hardware configuration:

Multi-writer replication has been a challenge in the MySQL ecosystem for years before truly dedicated solutions were introduced – first Galera (and so Percona XtradDB Cluster (PXC)) replication (around 2011), and then Group Replication (first GA in 2016).

Now, with both multi-writer technologies available, do we still need traditional asynchronous replication, set up in active-active topology? Apparently yes, there are still valid use cases. And you may need it not only when for some reason Galera/PXC or GR are not suitable, but also when you actually use them. Of course, the most typical case is to have a second cluster in a different …

Apologies for the silly title, but the issue is a real one, even though it is not a new thing. Schema upgrades are not an ordinary operation in Galera. For the subject at hand, the bottom line is: under the default Total Order Isolation (TOI) method, “the cluster replicates the schema change query as a statement before its execution.” What this means in practice is that a DDL issued in one node is replicated to other nodes in the cluster before it is even executed in the source node, let alone completed successfully.

As a result of this, it may fail in one node and be successful in another, and this without raising loud alerts or stopping nodes to protect against data inconsistency. This is not a bug in itself but rather a compromise of design. With new changes in MySQL and the …

MySQL databases keep getting larger and larger. And the larger the databases get, the harder it is to backup and restore them.  MyDumper has changed the way that we perform logical backups to enable you to restore tables or objects from large databases. Over the years it has evolved into a tool that we use at Percona to back up petabytes of data every day. It has several features, but the most important one, from my point of view, is how it speeds up the entire process of export and import.

Until the beginning of this year, the latest release was from 2018; yes, more than two years without any release. However, we started 2021 with release v0.10.1 in January, with all the merges up to that point and we committed ourselves to release every two months… and we delivered! …

MySQL Group Replication is a plugin that helps to implement highly available fault-tolerant replication topologies. In this blog, I am going to explain the complete steps involved in the below two topics.

• How to convert the group replication member to an asynchronous replica
• How to convert the asynchronous replica to a group replication member

Why Am I Converting From GR Back to Old Async?

Recently I had a requirement from one of our customers running 5 node GR clusters. Once a month they are doing the bulk read job for generating the business reports. When they are doing the job, it affects the overall cluster performance because of the flow control issues. The node which is executing the read job is overloaded and delays the certification and writes apply process. The read job queries can’t be split across the cluster.  So, they don’t want that …

While I was working on my grFailOver POC, I have also done some additional parallel testing. One of them was to see how online DDL is executed inside a Group Replication cluster.

The online DDL feature provides support for instant and in-place table alterations and concurrent DML. Checking the Group Replication (GR) official documentation, I was trying to identify if any limitation exists, but the only thing I have found was this:

“Concurrent DDL versus DML Operations.  Concurrent data definition statements and data manipulation statements executing against the same object but on different servers is not supported when using multi-primary mode. During execution of Data Definition Language (DDL) statements on an object, executing concurrent Data Manipulation Language (DML) on the …

Where x is >= 22

The Problem

There are few things your data does not like. One is water and another is fire. Well, guess what:

If you think that everything will be fine after all, take a look:

Given my ISP had part of its management infrastructure on OVH, they had been impacted by the incident.

As you can see from the highlight, the ticket number in three years changes very little (2k cases) and the date jumps from 2018 to 2021. On top of that, I have to mention I had opened several tickets the month before that disappeared. 

So either my ISP was very lucky and had very few cases in three years and sent all my tickets to /dev/null… or they have lost THREE YEARS of data.   

Let us go straight to the chase; they have lost their …

This blog provides high availability (HA) guidelines using group replication architecture and deployment recommendations in MySQL, based on our best practices.

Every architecture and deployment depends on the customer requirements and application demands for high availability and the estimated level of usage. For example, using high read or high write applications, or both, with a need for 99.999% availability.

Here, we give architecture and deployment recommendations along with a technical overview for a solution that provides a high level of high availability and assumes the usage of high read/write applications (20k or more queries per second).

Layout

Components

This architecture is composed of two main layers:

• Connection and distribution layer
• RDBMS …

Chasing bugs can be a tedious task, and multi-threaded software doesn’t make it any easier. Threads will be scheduled at different times, instructions will not have deterministic results, and in order for one to reproduce a particular issue, it might require the exact same threads, doing the exact same work, at the exact same time. As you can imagine, this is not straightforward.

Let’s say your database is crashing or even having a transient stall.  By the time you get to it, the crash has happened and you are stuck restoring service quickly and doing after-the-fact forensics.  Wouldn’t it be nice to replay the work from right before or during the crash and see exactly what was happening?

Record and Replay is a technique where we record the execution of a program allowing it to be replayed over and over producing the same result. Engineers at …