The latest from the MySQL community

     VIEWs have been a handy feature of MySQL for many years but do you know about the WITH CHECK OPTION clause?  The WITH CHECK OPTION clause is used for a updatable views to prohibit the changes to those views that would produce rows which are not included in the defining query.

    VIEW Definition    Since a lot of SQL novices read my blog, I'd like to start with the definition of a view "Views are stored queries that when invoked produce a result set. A view acts as a virtual table" according the MySQL Manual.
SQL > CREATE VIEW x_city AS             SELECT     Name,                        …

Question: Hey, I got a UNIQUE INDEX, but I can store multiple rows with the same value, NULL. That is surprising. Is that a bug?

This is a rewrite of the same in German from 9 years ago.

root@localhost [kris]> create table t ( a integer, b integer, unique (a,b));
Query OK, 0 rows affected (0.09 sec)

root@localhost [kris]> insert into t values (1, 2);
Query OK, 1 row affected (0.01 sec)

root@localhost [kris]> insert into t values (1, 2);
ERROR 1062 (23000): Duplicate entry '1-2' for key 't.a'

This does not work, as expected. But this does:

root@localhost [kris]> truncate table t;
Query OK, 0 rows affected (0.16 sec)

root@localhost [kris]> insert into t values ( 1, NULL);
Query OK, 1 row affected (0.02 sec)

root@localhost [kris]> insert into t values ( 1, NULL);
Query OK, 1 row affected (0.03 …

This is the updated and english version of some older posts of mine in German. It is likely still incomplete, and will need information added to match current MySQL, but hopefully it is already useful.

Old source articles in German: 1, 2 and 3.

Some vocabulary

Symbol, Font, Encoding and Collation - what do they even mean?

A character set is a collection of symbols that belong together. That is a completely abstract thing, and also almost useless. The only thing you can do with a character set is decide if a specific symbol is legal within a context or not. And, if it is legal, what position the …

 In a blog post I posted on the 16th of January I showed some graphs of CPU

usage, network usage and disk usage. The benchmark that was running was

a modified variant of YCSB (Yahoo Cloud Serving Benchmark) based on version

0.15.0 of YCSB.

In this blog post I will describe the setup of the NVMe drives for this

benchmark using DenseIO machines in the Oracle Cloud.

Oracle Cloud has a variety of machines available. In this benchmark we wanted

to show NDB with a database size of around 20 TByte of user data in a replicated

setup.

There are numerous ways to connect disk drives to Oracle Cloud machines. One

manner is to use block storage. In this case the actual storage is on separate …

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 …

I like bugs.  Probably not as much as Valerii Kravchuk (http://mysqlentomologist.blogspot.com/) a former colleague of mine who posted about MySQL bugs for a long time, but I still like bugs.  I like finding bugs, I like fixing bugs, and I like analyzing bugs.  

While I work on the WARP storage engine, I am filing bugs and feature requests for issues I find with MySQL.  I also like to comment on MySQL bugs in the bug database to help the MySQL engineers find root causes, and to help end users with workarounds, or explaining misconceptions as to why something may not be a bug.  So here are a few interesting bugs I have encountered recently.

Optimizer gives bad estimates for ICP query plans resulting in FTS:
https://bugs.mysql.com/bug.php?id=100471 …

In Percona Kubernetes Operator for Percona XtraDB Cluster (PXC) versions prior to 1.5.0, there were two methods for upgrading PXC clusters, and both of these use built-in StatefulSet update strategies. The first one is manual (OnDelete update strategy) and the second one is semi-automatic (RollingUpdate strategy). Since the Kubernetes operator is about automating the database management, and there are use cases to always keep the database up to date, a new smart update strategy was implemented.

Smart Update Strategy

The smart update strategy can be used to enable automatic context-aware upgrades of PXC clusters between minor versions. One of the use cases for automatic upgrades is if you want to get security …

    MySQL has had replication for decades but the various options can be confusing.  One social media post I read recently could be summarized with the statement 'there are too many good options but how do I know which is right for me?'

Cluster

    Of all the words used in the computer related world, 'cluster' is the one that I wish we could have found a replacement for as the confusion over the word has created it's own cluster. Since MySQL has InnoDB Cluster and NDB cluster with other vendors using the word we end up with a lot of confusion. Add in clustered indexes and other non replication uses of the word to add more confusion. So which is what and where do we apply then for best performance.

MySQL Replication 101

    The follow is an overview of MySQL replication offerings and the details are in the manual.  And of course there are third party software that …

Rewriting a MySQL query for performance is an important process that every DBA should be aware of so they can fix the wrong queries on runtime without code changes on the application end. ProxySQL has great support for rewriting the queries, which Alkin Tezuysal already explored in his excellent blog ProxySQL Query Rewrite Use Case.

So far, MySQL community provides two built-in query rewrite plugins to perform this task. Recently they introduced the plugin “ddl_rewriter”.

• query rewriter plugin : It has support for INSERT / UPDATE / DELETE / REPLACE statements from MySQL 8.0.12. 
• ddl_rewritter plugin: It supports the CREATE TABLE statement. Introduced at MySQL 8.0.16.

In this blog, I am going to explain the complete process of the implementation and the …

Recently I had the opportunity to test a storage device from ScaleFlux called CSD 2000. In this blog post, I will share the results of using it to run MySQL in comparison with an Intel device that had a similar capacity.

First of all, why do we need another storage device? Why is ScaleFlux any different?

The answer is simple; it gives us built-in compression and atomic writes. For many workloads, but especially for database-type workloads, these are very important features.

Because of built-in compression, we can store more data on the ScaleFlux device than on a similar device with the same capacity.

Because of atomic writes, we can disable InnoDB Double Write buffer which means less writes/fsync on the disk layer. This should give us a performance advantage against non-atomic drives.

I ran many different tests on different data sizes, with different …