The latest from the MySQL community

Well, let me say if that happens it’s because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short, the WHY of this article is to inform you about possible pitfalls and how to prevent them from causing you damage.

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from the MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing …

Well, let me say if that happens because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short the WHY of this article is to inform you about possible pitfalls and how to prevent that to cause you damage. 

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing queries at the …

Well, let me say if that happens because there is a logic mistake in your application. But you need to know and understand what happens in MySQL to be able to avoid the problem. 

In short the WHY of this article is to inform you about possible pitfalls and how to prevent that to cause you damage. 

Let us start by having a short introduction to what Repeatable reads are about. Given I am extremely lazy, I am going to use (a lot) existing documentation from MySQL documentation.

Transaction isolation is one of the foundations of database processing. Isolation is the I in the acronym ACID; the isolation level is the setting that fine-tunes the balance between performance and reliability, consistency, and reproducibility of results when multiple transactions are making changes and performing queries at the …

At work, replication

is a central feature in our MySQL Standard Architecture.

But until MySQL 5.6, replication was strictly sequential: Even if transactions happened in parallel on a primary, they would be downloaded to the replica by the IO_THREAD into the relay log. From there, a single SQL_THREAD would apply them, one after the other in strict binlog order. That can lead to Replication Delay.

We had a monitor for that, courtesy of Dennis Kaarsemaker

. That code looked at the time consumption in the SQL_THREAD, and counted the percentage of idle time over time, visualizing it in Graphite or Grafana.

This was the amount of runway we had. If the write-load to a specific replication hierarchy threatened to …

Part 1

What is a GTID? Oracle/MySQL define a GTID as "A global transaction identifier (GTID) is a unique identifier created and associated with each transaction committed on the server of origin (the source). This identifier is unique not only to the server on which it originated, but is unique across all servers in a given replication topology."

An errant transaction can make promotion of a replica to primary very difficult.

An errant transaction is BAD. Why is it bad? The errant transaction could still be in the replicas binlog so when it becomes the new primary these event will get sent to other replicas causing data corruption or breaking replication.

Its easy to prevent errant transaction.

1. read_only = ON in the replicas my.cnf
2. Disable binlogs when you need to perform work on a replica. set session sql_log_bin = 'off'; before your work on replica. …

As an example for my class on the usefulness of Common Table Expressions (CTEs), I created three examples with Python. They extend an exercise in Chapter 9 on subqueries from Learning SQL by Alan Beaulieu. All of the examples work with the sakila sample database.

These bullets describe the examples:

1. Uses local variables and a range for loop and if statement that uses the variables to evaluate and add an element to the derived table (or query result set) from MySQL.
2. Uses a CTE with substitution variables from the Python program, which eliminates the need to evaluate and add an element to the query result set because the query does that.
3. Uses a table to hold the variables necessary to evaluate and add the element to the query result set.

This is the first Python program:

# Import the library.
import sys
import …

Query planning is hard # Have you ever wondered what goes on behind the scenes when you execute a SQL query? What steps are taken to access your data? In this article, I'll talk about the history of Vitess's V3 query planner, why we created a new query planner, and the development of the new Gen4 query planner. Vitess is a horizontally scalable database solution which means that a single table can be spread out across multiple database instances.

This is a new era in deploying, managing and monitoring your Galera Cluster for MySQL, with the recently released Galera Manager, now Generally Available (GA). Galera Manager is a web-based graphical user interface (GUI) tool that allows you to fully manage clusters in Amazon Web Services, you can also deploy clusters on user provided hosts (on premise or in the cloud) and you can also fully monitor your existing clusters.

In this Webinar, we will cover:

• Deploying a fully managed cluster in AWS
• Deploying a cluster on user-provided hosts
• Monitoring an existing cluster
• How we have chosen to use CLONE SST for MySQL 8 deployments
• How you can successfully deploy all the various servers that we support
• Utilising the over 600 monitoring metrics to effectively manage your Galera Cluster

…

Running Java in the cloud helps lower costs, speed up operations, and simplify the deployment.

Running Java in the cloud helps lower costs, speed up operations, and simplify the deployment.