The latest from the MySQL community

From MySQL 5.7, we had a Multi-threaded Slave (MTS) Applier mechanism called LOGICAL_CLOCK to overcome the problems of parallel replication within a database.

To further improve the parallelisation mechanism, from MySQL 8 (5.7.22) we have write-set replication, so before going further , lets look at the difference between Logical clock (LC) and Writeset.

LOGICAL_CLOCK

Transactions that are part of the same binary log group commit on a master are applied in parallel on a slave. The dependencies between transactions are tracked based on their timestamps to provide additional parallelisation where possible.

WRITESET

Write-set is a mechanism to track independent transactions that can be executed in parallel in the slave. Parallelising on write sets has potentially much more parallelism than logical_clock ,since it does not depend …

The goal of this blog post is to explain the various types of transaction isolation levels available in MySQL. After reading the blog, you will be able to explain dirty reads, non-repeatable reads, and the concept of phantom rows as well.

What is the Isolation Level in MySQL?

Isolation (I) is one of the properties from ACID. It defines how each transaction is isolated from other transactions and is a critical component of application design. As per the SQL:1992 standard, InnoDB has four types of Isolation levels. Below, I have listed the types in order, and each transaction isolation level provides better consistency compared to the previous one.

• READ-UNCOMMITTED
• READ-COMMITTED
• REPEATABLE-READ – ( MySQL’s DEFAULT )
• SERIALIZABLE

You can change the isolation level using the variable “transaction_isolation” at runtime. As transaction isolation changes can …

Hi and thanks to all who attended my webinar on Tuesday, January 26th titled Using PMM to Identify & Troubleshoot Problematic MySQL Queries!

Like we do after all our webinars, we compile the list of questions that were answered verbally and also those that were posed yet remained unanswered since we ran out of time during the broadcast.  Before we get to the questions, I wanted to make sure to include a link to the RED Method for MySQL Queries by Peter Zaitsev, Percona’s CEO:

https://grafana.com/grafana/dashboards/12470

Hi Michael, you suggested that table create and update times should be ignored. Surely these values come from information_schema.tables? Does that not reflect what I would see if I …

Query attributes have in a long time been used to add metadata to queries to provide additional context such as where in the application the query was generated. The traditional way to do this is to add a comment at the start of the query with the attributes. Since the MySQL parser ignores the comment, it does not change the semantics of the query, but various tools can extract the comments.

This post looks into the reasons for using query attributes, how it is done using a comment, and the new component for MySQL 8.0.23 that provides native support for query attributes.

Advice

Query attributes are also known as query tags.

Why Query Attributes?

At the surface, it may seem that there is no major benefit from having metadata attached to a query – after all it is ignored by MySQL. However, there are good reasons. The …

In March 2020, my book MySQL 8 Query Performance Tuning (Apress) was released. That book with its more than 900 pages in 27 chapters covered a wide range of topics from executing benchmarks with sysbench over indexes and the optimizer to query rewriting, replication, and caching. Some time later my editor Jonathan Gennick suggested to take a limited set of the topics and go into more detail. We settled on locks and transactions which together have become MySQL Concurrency.

If you have already read MySQL 8 Query Performance Tuning, you may wonder what the new book offers compared to the previous one. In some way, you can think of MySQL Concurrency to be a second and expanded edition for the content on locks and transactions. Of course, given MySQL Concurrency is limited to those two topics, it has also been …

There was an excellent question from Francis on my MySQL X DevAPI tutorial on how to work with NULL values:

Is it possible to store an attribute with the null value, and how to find it (xxx is null ?

It may sound like a trivial question, but the answer is not all that simple, so instead of just replying directly to the comment, I think it is worth covering the subject of NULL values in the X DevAPI in a separate post.

The Short Story

In short there are two ways to work with “not a value” in the X DevAPI. One way is to not set a value for those fields in which case you can compare the retrieved values with IS NULL as you would for a relational table, for example in MySQL Connector/Python:

# Find documents where "Birthday IS NULL"
stmt_find = …

We recently saw how the new Invisible Column feature works in MySQL since 8.0.23 and how we can use it as a Primary Key for InnoDB tables when no Primary Key was defined.

As I wrote earlier, a good Primary Key is important for InnoDB (storage, IOPS, secondary indexes, memory…) but there is another important domain where a Primary Key is important in MySQL: replication !

Asynchronous Replication

When using “traditional” replication, if you modify a record (UPDATE and DELETE), the record(s) to modify on the replica are identified using indexes, and of course the Primary Key if any. The hidden global 6-bytes auto generated by InnoDB primary key is never used as never exposed and as it’s global, …

This article is the second part of the series related to MySQL Invisible Column started here.

This post covers why Invisible Column is important for InnoDB Storage Engine.

To start, let me explain briefly how InnoDB deals with Primary Key and why an good primary key is important. And finally, why having a Primary Key is also important.

How does InnoDB Stores Data?

InnoDB stores data in table spaces. The records are stored and sorted using the clustered index (the primary key): they are called index-organized tables.

All secondary indexes also contain the primary key as the right-most column in the index (even if this is not exposed). That means when a secondary …

As a continue of the regular blog posts informing you about where you can find MySQL Community & MySQL team at, please find below a list of shows you can join and listen MySQL talks & sessions. 

• January 2021:

  • Coud Native Meetup/VIRTUAL, January 26, 2021 - URL to be provided later on.
    • Frederic Descamps, the MySQL User Group Manager will talk on: "MySQL 8.0: Why to use MySQL 8.0 and how to deploy a web application in OCI using MySQL Database Service" 
    • Scheduled for January 26th as EMEA & JAPAC session & January 27th, 2021.
  • OpenSource Conference Osaka/VIRTUAL, January 30, 2021
    • Yoshiaki Yamasaki, the MySQL …

Dear MySQL users,

MySQL Shell 8.0.23 is a maintenance release of MySQL Shell 8.0 Series (a
component of the MySQL Server). The MySQL Shell is provided under
Oracle’s dual-license.

MySQL Shell 8.0 is highly recommended for use with MySQL Server 8.0 and
5.7. Please upgrade to MySQL Shell 8.0.23.

MySQL Shell is an interactive JavaScript, Python and SQL console
interface, supporting development and administration for the MySQL
Server. It provides APIs implemented in JavaScript and Python that
enable you to work with MySQL InnoDB cluster and use MySQL as a document
store.

The AdminAPI enables you to work with MySQL InnoDB cluster and InnoDB
ReplicaSet, providing integrated solutions for high availability and scalability
using InnoDB based MySQL databases, without requiring advanced MySQL
expertise.  For more …