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Displaying posts with tag: Insight for DBAs (reset)
Digital Signatures: Another Layer of Data Protection in Percona Server for MySQL

Imagine you need to design an online system for storing documents on a per-user basis where nobody, including database administrators, would be able to change the content of those documents without being noticed by document owners.

In Percona Server for MySQL 8.0.28-20, we added a new component called Encryption UDFs – an open-source alternative to MySQL Enterprise Encryption that allows users to access a number of low-level OpenSSL encryption primitives directly from MySQL. This includes calculating digests (with a great variety of hash functions), asymmetric key generation (RSA, …

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MyDumper’s Stream Implementation

As you might know, mysqldump is single-threaded and STDOUT is its default output. As MyDumper is multithreaded, it has to write on different files. Since version 0.11.3 was released in Nov 2021, we have the possibility to stream our backup in MyDumper. We thought for several months until we decided what was the simplest way to implement it and we also had to add support for compression. So, after fixing several bugs, and we now consider it is stable enough, we can explain how it works.

How Can You Stream if MyDumper is Multithreaded?

Receiving a stream is not a problem for myloader, it receives a file at a time and sends it to a thread to process it. However, each worker thread in mydumper is connected to the database, and as soon as it reads data, it should be sent to the stream, which might cause collisions with other worker threads that are reading data from the database. In order to avoid this issue, we ended up with the …

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Session Temporary Tablespaces and Disk Space Usage in MySQL

Temporary Tables handling in MySQL has a somewhat checkered past. Some time ago, my colleague Przemek wrote a post about differences in the implementations between versions of MySQL. If you are looking for the differences in implementation, that’s a perfect place to check.

In this post, I’d like to focus on Session Temporary Tablespaces, InnoDB on-disk internal temporary tables that come to play when a query requires storing more data than tmp_table_size or TempTable engine allocated more than …

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Is MySQL Statement-Based / Mixed Replication Really Safe?

The binary logging format in MySQL has been ROW by default since MySQL 5.7, yet there are still many users sticking with STATEMENT or MIXED formats for various reasons. In some cases, there is just simple hesitation from changing something that has worked for years on legacy applications. But in others, there may be serious blockers, most typically missing primary keys in badly designed schemas, which would lead to serious performance issues on the replicas.

As a Support Engineer, I can still see quite a few customers using STATEMENT or MIXED formats, even if they are already on MySQL 8.0. In many cases this is OK, but recently I had to deal with a pretty nasty case, where not using ROW format was found to cause the replicas to silently lose data updates, without raising any replication errors! Was it some really …

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Looking for an Excellent MySQL Book for Beginners? The MySQL Workshop is a Great Choice

Last week at Percona Live, I was asked what book I recommend for novices seeking to learn MySQL.  For a long time, there has not been a good choice for modern versions of MySQL. Luckily I had just stumbled upon such a book.  Now I am happy to recommend The MySQL Workshop – A practical guide to working with data and managing databases with MySQL by Petit and Cosentino.

The first chapter introduces database architectures, data types, storage engines (including MyRocks), and data normalization. The following chapter cover in great detail how to create a database, using MySQL Workbench, backups & restoring data, and creating indexes. Chapter four has a very good section on working with SQL, functions, and case statements. Then JOINs and stored procedures are covered.

In another book, that would probably be enough content, but later chapters plunge into using Node.JS, Access, and Excel with …

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Securing Dynamic Log File Locations in MySQL

MySQL allows changing the location of the general log and the slow query log while the server is running by anybody having the SYSTEM_VARIABLES_ADMIN privilege to any location, including appending to existing files. In Percona Server for MySQL 8.0.28-19 we introduced a new system variable, secure-log-path, that can be used to restrict the location of these log files to avoid accidents or possible data corruption attacks.

When somebody with the system variables admin privilege changes these variables, the server runs a few sanity checks. Unfortunately, these checks are quite minimal, and only verify that the specified file is writable by mysqld.

Compared to this, other variables specifying write-related file and directory names are either read-only during the runtime of the server (such as datadir, tmpdir, or log_error), or have additional …

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A Quick Peek At MySQL 8.0.29

Oracle released MySQL Server 8.0.29 on April 26th and this is a quick review of the release notes.  I have put my own comments in italics.

So what is in the ’29 release of MySQL Server?  Does it come festooned with new, neat features or is it a big bug-fix bonanza?


While this server release has some interesting stuff, there is no compelling feature that will necessitate an immediate upgrade.  Read through the release notes to see if anything in there that is a must for you but for most of us, MySQL 8.0.29 does not require an immediate update.  If this was a birthday or holiday present, ’29 is the equivalent of getting a fresh box of dental floss – useful but not thrilling.

The shell is evolving too and the new version for VS Code looks promising.

MySQL Server 8.0.29 UTF8MB3?

The server now makes extensive use of UTF8MB3 (yes 3, not …

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Zero Impact on Index Creation with Amazon Aurora 3

In the last quarter of 2021, AWS released Aurora version 3. This new version aligns Aurora with the latest MySQL 8 version, porting many of the advantages MySQL 8 has over previous versions.

While this brings a lot of new interesting features for Aurora, what we are going to cover here is to see how DDLs behave when using the ONLINE option. With a quick comparison with what happens in MySQL 8 standard and with Group Replication.


All tests were run on an Aurora instance r6g.large with a secondary availability zone. The test was composed of:

        Four connections

    • #1 to perform DDL
    • #2 to perform insert data in the table I am altering
    • #3 to perform insert data on a different table 
    • #4 checking the other node operations

In the Aurora instance, a …

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Finding Differences Between MySQL Servers

When one is responsible for promoting application development from Dev through the various environments such as QA, UAT, etc., through Production, it is often useful to ensure that configurations in test environments are comparable to the final production environment.  This is especially true with systems where a team of DBAs manage the servers.

Obviously, the difference in performance could be due to differences in hardware, storage, networking, software configuration, etc.  The question is how does one quickly and efficiently find the differences without having to run a lot of different commands and compare the output.  Fortunately, our Percona Toolkit has a couple of utilities that can make this much easier.  When you are tasked with supporting large numbers of servers, efficiency is paramount and this is where the toolkit can really help you!

You can find more information on the Percona Toolkit here: …

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Correcting MySQL Inaccurate Table Statistics for Better Execution Plan


By diving into the details of our case study, we will explain how incorrect table statistics may lead the optimizer to choose a suboptimal execution plan. We will also go into how MySQL calculates the table statistics and the ways to correct the table statistics to prevent it from happening again.

Case study: Incorrect table statistics lead the optimizer to choose a poor execution plan.

A customer reported a drastic performance degradation of a query while there were no code changes and no configuration changes made. The data in this article has been edited for brevity and modified to mitigate the exposure of confidential information. The case has also been approved for publication by the customer.

We obtained the query execution plan, and got the results as shown below (execution plan #1):

mysql> explain 
-> SELECT count(          ,
->        MAX(DAYNAME( ,
-> …
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