The latest from the MySQL community

Codership is pleased to announce a new Generally Available (GA) release of the multi-master Galera Cluster for MySQL 5.7, consisting of MySQL-wsrep 5.7.40 (release notes, download) and MySQL-wsrep 8.0.31 (release notes, download) with Galera replication library 4.14 (release notes, download) implementing wsrep API version 26. …

ProxySQL is an open-source MySQL proxy server, meaning it serves as an intermediary between a MySQL server and the applications that access its databases. ProxySQL can improve performance by distributing traffic among a pool of multiple database servers.

Consider 2 slaves are routed under Proxysql , In any one of the slave, if the replication is broken, we could still see the traffic routing to the broken replication slave. We can make Proxy to not send traffic to broken replication slave, by setting appropriate value to the variable mysql-monitor_slave_lag_when_null

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This post was originally published in October 2018 and was updated in March 2023.

pt-query-digest is one of the most commonly used tools for query auditing in MySQL. By default, pt-query-digest reports the top ten queries consuming the most amount of time inside MySQL. A query that takes more time than the set threshold for completion is considered slow, but it’s not always true that tuning such queries makes them faster. Sometimes, when resources on the server are busy, it will impact every other operation on the server, and so will impact queries too. In such cases, you will see the proportion of slow queries going up. That can also include queries that work fine in general.

This article explains a small trick to identify such spots using pt-query-digest and the slow query log. pt-query-digest …

Hello friends, at Percona Managed Services, we usually do different types of things every day, including routine tasks, monitoring, and, very frequently, answering questions that are not always easy to answer.

A few days ago, a client asked us the following question: “Hey Percona, I have a question and a problem simultaneously: I want to delete rows from a table from a specific date back because the data is not necessary. I tried to run the DELETE command, which gave me this error: Cannot delete or update a parent row: a foreign key constraint fails. Could you please help me?”

At first glance, the error message was obviously clear: the table from which rows were to be deleted had a child table, which prevented the execution of the DELETE directly.

“Don’t worry, we’ll take a look at the issue, and …

Introduction/TLDR:

We are considering changing EXPLAIN in Percona Server for MySQL to require less privileges for providing execution plans for INSERT/UPDATE/DELETE statements (and possibly changing the behavior for EXPLAIN SELECT as well), to make it more convenient and safer to use with monitoring and query analysis tools. We would like to get feedback from the Community about the different approaches for achieving this.

The problem:

Running EXPLAIN is a great way to understand how complex SQL statements are executed. So it is natural that monitoring and query analysis tools utilize EXPLAIN for these purposes.

However, there is a problem for cases when INSERT/UPDATE/DELETE statements need to be explained. Running EXPLAIN for these statements, a read-only operation, requires the same privileges as running the original statements …

Given a table named tbl with one million entries, we want to select a random row from this table, fast. Our table definition looks like this:

create table tbl (
    id INTEGER NOT NULL,
    d VARCHAR(200) NOT NULL,
    INDEX(id)
);

Dense id space

We can generate some test data using a recursive CTE:

mysql> set cte_max_recursion_depth = 100000;
mysql> insert into tbl 
    -> with recursive c(n, u) as (
    ->   select 1, uuid() 
    -> union all
    ->   select n+1, uuid() from c where n < 100000
    -> ) select * from c ;

The Recursive CTE will generate 100k pairs of (number, uuid()). The initial row is defined in the upper row of the UNION, each subsequent row builds recursively on top of that, by simply counting …

Given a table named tbl with one million entries, we want to select a random row from this table, fast. Our table definition looks like this:

create table tbl (
 id INTEGER NOT NULL,
 d VARCHAR(200) NOT NULL,
 INDEX(id)
);

Dense id space

We can generate some test data using a recursive CTE:

mysql> set cte_max_recursion_depth = 100000;
mysql> insert into tbl
 -> with recursive c(n, u) as (
 -> select 1, uuid()
 -> union all
 -> select n+1, uuid() from c where n < 100000
 -> ) select * from c ;

The Recursive CTE will generate 100k pairs of (number, uuid()). The initial row is defined in the upper row of the UNION, each subsequent row builds recursively on top of that, by simply counting up.

Since we generate …

Thank you to everyone who joined us for the 19th edition of MyWebinar. We hope that our time together helped to elevate and seam your work to perfection. We’re committed to giving back to the opensource database community in the coming days by presenting more LIVE events.

Recently, Mydbops conducted a webinar on the top 10 features of MySQL 8. MySQL is one of the most popular and widely used open-source relational database management systems. With every new version, MySQL brings new features and enhancements that make it more reliable, secure, and efficient. In this blog, we will wrap up the top 10 features of MySQL 8 discussed in the webinar by Mydbops.

Vinoth Kanna, co-Founder from  …

Percona XtraBackup is an open source hot backup utility for MySQL-based servers. To take consistent and hot backup, it uses various locking methods, especially for non-transactional storage engine tables. This blog post discusses the cause and possible solution for queries with ​Waiting for table flush state in processlist when taking backups using Percona XtraBackup. Only MySQL 5.7 version is affected by this, as per my tests.

Type of locks taken by Percona XtraBackup

Before discussing the main issue, let’s learn about the type of locks used by Percona XtraBackup to take consistent backups. Percona XtraBackup uses backup locks as a lightweight alternative to FLUSH TABLES WITH READ LOCK. This feature is …

I discovered a dependency for MySQL Workbench on AlmaLinux 8 installation. I neglected to fully cover it when I documented the installation in a VM of AlmaLinux 9. I go back later and update that entry but for now you need the following dependencies:

proj-6.3.2-4.el8.x86_64.rpm
proj-datumgrid-1.8-6.3.2.4.el8.noarch.rpm
proj-devel-6.3.2-4.el8.x86_64.rpm

Install like this:

sudo dnf install -y *.rpm

Log file:

Last metadata expiration check: 3:01:53 ago on Fri 10 Feb 2023 03:37:49 AM UTC.
Dependencies resolved.
==========================================================================================
 Package                Architecture   Version                 Repository            Size
==========================================================================================
Installing:
 proj                   x86_64         6.3.2-4.el8             @commandline         2.0 M
 proj-datumgrid         noarch …