At Percona Live Online my colleague at Alibaba, Jim Tommaney, presented a study of hash join performance in MySQL and Marwho?iaDB. For some of the queries, the peformance characteristics for MySQL seemed a bit strange, and I decided to look closer into what was going on. As you can read below, I found that the crucial point was the memory usage of hash join in MySQL.

Results presented at Percona Live ONLINE

In Jims presentation, you can see the following graphs for the performance of his query 2.2 on MySQL and Marwho?iaDB:

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After I updated a Fedora 30 instance, I could no longer connect to the MySQL database. An attempt to connect raised the following error:

Error: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)

My guess was correct, the mysqld.service got removed during the update (a synonym for upgrade). So, I ran the following command as a sudoer user:

sudo systemctl enable mysqld.service

It creates the following symbolic link:

Created symlink /etc/systemd/system/multi-user.target.wants/mysqld.service → /usr/lib/systemd/system/mysqld.service.

That would start the MySQL Daemon (mysqld) on the next restart of the OS. However, I didn’t want to restart to have access to the service. I simply started it with the following command:

sudo systemctl start mysqld.service

Then, I could connect to the MySQL database. As always, …

As the name indicates, an undo log record contains information about how to undo the recent changes by a transaction. When a transaction writes data, it always makes writes on the tablespace files. InnoDB Undo log stores copy of data that is being modified by any current transaction. So, at this point in time if any other transaction queries for the original data (row) which is being modified,  the undo logs provide the same and serve the purpose. This is what provides a consistent read view ( based on isolation ) during any data modifications.

Here in the above representation, Transaction T1 modifies the data (Data-1). During the time of modification to ensure the reads are consistent, transactions T2  and T3 are given access only to the copy (previous row version) of Data -1 which is stored in the “UNDO” …

In this continuing series of posts of fundamental DBA security tasks,  we will look at passwords again, the good, the bad and the outright ugly. This group of tasks will help you find insecure users with poor passwords and provide … Continue reading →

    The new MySQL Shell or mysqlsh has provisions for loading user plugins in Python or JavaScript that are loaded when the shell starts up. I am just taking my initial steps into this area and wanted to share with you how easy it is to create a plug-in to produce a report.
    The ability to write and run your own scripts for information that you want on a regular basis is very useful. The idea behind this was a discussion with a community member who had issues with a locked account that unknowingly locked and knowing when passwords where changed.  This is a typical bit of work for a DBA that would be better automated and saved as a script for future uses.
The Query
    The query collects several vital facets of information for dealing with passwords and accounts.
SELECT concat(User, '@',Host) as User,       …

Usually, database people are familiar with table fragmentation with DELETE statements. Whenever doing a huge delete, in most cases, they are always rebuilding the table to reclaim the disk space. But, are you thinking only DELETEs can cause table fragmentation? (Answer: NO).

In this blog post, I am going to explain how table fragmentation is happening with the INSERT statement.

Before going into the topic, we need to know that with MySQL, there are two kinds of fragmentation:

• Fragmentation where some of the InnoDB pages are completely free inside the table.
• Fragmentation where some of the InnoDB pages are not completely filled (the page has some free space).

There are three major cases of table fragmentation with INSERTs :

• INSERT with ROLLBACK
• Failed INSERT statement
• Fragmentation with page-splits

…

In this post, I’ll cover examples of the MySQL TRIM() function. TRIM() removes specific characters – or spaces – from a given string, at either: the beginning, ending, or potentially in both locations depending on several factors. With an optional keyword argument that controls which character(s) – if any – are removed, TRIM() can be tricky so let’s gain understanding with several easy-to-digest examples…

Photo by Peter Beukema on Unsplash

OS, Software, and DB used:

• OpenSuse Leap 15.1
• MySQL 8.0.20

Self-Promotion:

If you enjoy …

A few days ago, a customer got in touch asking how they could use Percona Monitoring and Management (PMM) to monitor the roles played by each node in an InnoDB cluster. More specifically, they wanted to check when one of the nodes changed its role from Primary to Secondary, or vice-versa. PMM allows for a high level of flexibility and customization through its support for custom queries, and we just have to be creative on how we approach the problem. In this post, we present the steps we did to test our solution, including the deployment of a 3-node InnoDB Cluster hosted in the same server (for testing) and a PMM 2 server, and connecting them together. Even though this has already been covered in other blog …

Watch our latest on-demand webinar: Deploying Hybrid & Multi-Cloud Applications With Ultimate MySQL Availability. Learn about the pros and cons of single cloud region vs multi-region cloud deployments … and more.

Tags:  MySQL Cloud hybrid cloud Multi-Cloud Webinar High Availability tungsten clustering …

Passwords lists abound on the net. They exist to: Get a laugh out of silly passwords… 123456 anyone? Develop a dictionary file to check user passwords either for validation or cracking. From MySQL 5.6 the validate_password plugin has been available. … Continue reading →