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Displaying posts with tag: Insight for Developers (reset)
Extensibility in MySQL Is Easy

Well, “easy” if you know just a tiny bit of C++.

MySQL is well known for its ease of use, being easy to install, easy to configure, and easy to maintain. What if there is something more that you’d like MySQL to do? How would you integrate some new fancy processing library into MySQL without having to recreate the complexities in pure SQL?

MySQL Loadable Functions would be the way to go. In this blog post, you’ll learn how to set up a build environment for compiling your own MySQL plugin to be loaded into MySQL as a function. Our function will implement a ULID generator using a C++ library from ChrisBove/ulid.

Creating the build environment

The first step is downloading the …

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An Overview of Indexes in MySQL 8.0: MySQL CREATE INDEX, Functional Indexes, and More

This blog was originally published in January 2022 and was updated in July 2023.

Working with hundreds of different customers, I often face similar problems around running queries. One very common problem when trying to optimize a database environment is index usage. A query that cannot use an index is usually a long-running one, consuming more memory or triggering more disk iops.

A very common case is when a query uses a filter condition against a column that is involved in some kind of functional expression. An index on that column can not be used.

Starting from MySQL 8.0.13, functional indexes are supported. In this article, I will first explain an overview of indexes in MySQL and cover the MySQL CREATE INDEX before diving into showing what functional indexes are and how they work.

Introduction to MySQL Indexes

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The Impacts of Fragmentation in MySQL

Fragmentation is a common concern in some database systems. Highly fragmented tables can affect performance and resource allocation. But reducing fragmentation often involves rebuilding the table completely. This blog post will discuss fragmentation and its impact on InnoDB.

What is fragmentation?

We say that something is fragmented when it is formed by parts that are separate or placed in a different order than the natural one. In databases, we can experiment with different types of fragmentation:

  • Segment Fragmentation: segments are fragmented; they are stored not following the order of data, or there are empty pages gaps between the data pages.
  • Tablespace Fragmentation: the tablespace is stored in non-consecutive filesystem blocks.
  • Table Fragmentation: data is stored not following the primary key order (heap tables), …
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Process MySQL LIMIT & ORDER BY for Performance Optimization

Updated June 1, 2023.

Suboptimal MySQL ORDER BY implementation, especially together with MySQL LIMIT is often the cause of MySQL performance problems. Here is what you need to know about MySQL ORDER BY LIMIT optimization to avoid these problems.

Try Now: Free your applications with Percona Distribution for MySQL

MySQL LIMIT clause

The MySQL LIMIT clause is a valuable tool for controlling the number of rows returned by a SELECT statement. By specifying the maximum number of rows to retrieve from the result set, it enables you to work with subsets of data, especially in situations involving large tables. This feature enhances query performance and optimizes resource usage by fetching only …

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MySQL 5.7 Upgrade Issue: Reserved Words

MySQL 5.7 reaches End of Life status this October. If you still need to start your migration, time is getting short. The first step for many is looking into the new reserved words in MySQL 8.0. As MySQL gets new functionality or the project matures, there are new additions to the list of reserved words you can not use as column names.

Reserved words added to 8.0

There is a list of the new reserved words later in this document that you need to review.

Odds are you are not using a column named Master_tls_ciphersuites, but what about Rank, System, Skip, or Lead? Those are a lot more common and may be in your table definitions, so your upgrade process will be harder. It is recommended that you use the util.checkForServerUpgrade() in the MySQL Shell to check for these Reserved Words.

So what happens if I use a reserved word?

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A Workaround for The “RELOAD/FLUSH_TABLES privilege required” Problem When Using Oracle mysqldump 8.0.32

In MySQL Server 8.0.32, Oracle fixed Bug #105761:

“mysqldump make a non-consistent backup with ‐‐single-transaction option” (this commit)

which caused a wave of complaints from users who could no longer do backups with the mysqldump utility because of the lack of the required privileges.

  • Bug #109701 “Fix for #33630199 in 8.0.32 introduces regression when ‐‐set-gtid-purged=OFF”
  • Bug #109685 “mysqldump has incompatible change in MySQL 8.0.32″

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Replication Issues and Binlog Compressor

You might want to use binlog compression with MySQL/Percona Server for MySQL, but it can come with drawbacks. This article discusses the need for using binlog compression and the potential issues it may cause.

Binlog compression is a technique used to reduce the size of binary log files, which can become quite large over time. This can be especially important in situations where disk space is limited. However, it’s important to be aware that using binlog compression can also cause issues with replication.

Consider the following scenario: you have restored a backup that was taken from a replica node using Percona XtraBackup. Once the restoration is complete, you want to set up replication using the information from the xtrabackup_slave_info …

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MySQL 8.0.31 added INTERSECT and EXCEPT to augment the long-lived UNION operator. That is the good news. The bad news is that you have to be careful using the EXCEPT operator as there is a trick.

Let’s start with some simple tables and load some simple data.

SQL > create table a (id int, nbr int);
Query OK, 0 rows affected (0.0180 sec)
SQL > create table b (id int, nbr int);
Query OK, 0 rows affected (0.0199 sec)
SQL > insert into a (id,nbr) values (1,10),(3,30),(5,50),(7,70);
Query OK, 4 rows affected (0.0076 sec)

Records: 4  Duplicates: 0  Warnings: 0
SQL > insert into b (id,nbr) values (1,10),(2,20),(3,30),(4,40);
Query OK, 4 rows affected (0.0159 sec)

Records: 4  Duplicates: 0  Warnings: 0

So each table has four rows of data with two rows – (1,10) and (3,30) – appearing in both.

SQL > select id,nbr from a;
| id | nbr |
|  1 |  10 |
|  3 |  30 |
|  5 |  50 |
|  7 |  70 | …
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Set Theory in MySQL 8.0: UNION and Now INTERSECT and EXCEPT

Are you familiar with the UNION statement for your SQL queries? Most likely, you are. It has been supported for a long time.

In case you are not familiar with UNION, don’t worry, I’m going to show you how it works with simple examples.

Considering “Set Theory”, other than the UNION, starting from the newly deployed MySQL Community 8.0.31, a couple of new clauses are available: INTERSECT and EXCEPT.

From now on you can rely on more powerful options to write your queries and deploy some Set Theory logic.

In this article, I’m going to present how the three options work.

The traditional UNION

UNION combines the results from two or multiple SELECT statements into a single result set. Let’s suppose you have two queries, A and B, they return the same number of columns with the same data types and you need to merge all rows from both queries into a single result set. You can …

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A Quick Peek at MySQL 8.0.31

Oracle releases updates to MySQL on a quarterly basis and the Release Notes for 8.0.31 arrived just before the software.  This time around there are some very interesting new features that will be handy including SQL standards support, as well as over 130 bug fixes.

The TL;DR:  Some nice new features but nothing spectacular.

  • FULL is now a reserved word.
  • InnoDB now supports parallel index builds, which improves index build performance. In particular, loading sorted index entries into a B-tree is now multithreaded.
  • The OpenSSL library for MySQL Server has been updated to version 1.1.1q.
  • The optimizer has been improved so that the old ER_NOT_SUPORTED_YET is not thrown when you try something like this:
        ((SELECT a, b, c FROM t ORDER BY a LIMIT 3) ORDER BY b LIMIT 2) ORDER …
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