As we’ve communicated in our blog post in May, the TokuDB Storage Engine has been marked as “deprecated” in Percona Server for MySQL 8.0. It will be removed in a future version (Percona Server for MySQL 8.0.28, expected to ship in Q1 2022).

With the release of Percona Server for MySQL 8.0.26, the storage engine will still be included in the binary builds and packages but will be disabled by default. If you are upgrading from a previous version, the TokuDB Storage Engine plugin will fail with an error message at server startup if it is installed.

You will still be able to re-enable it manually so that you can perform the necessary migration steps.

Re-enabling the TokuDB …

Back in December 2018, when we announced the general availability of Percona Server for MySQL 8.0, we also announced that the TokuDB Storage Engine has been marked as “deprecated” in this release, recommending to use the MyRocks Storage Engine as an alternative. We believe that MyRocks provides similar benefits for the majority of workloads and is better optimized for modern hardware.

Since then, we have continued maintaining the storage engine in the 8.0 release, e.g. by incorporating bug fixes. However, the ongoing amount of …

There is a common pattern in life, you often discover or understand things by accident. Many scientific discoveries fit such a description. In our database world, I was looking to see how BLOB/TEXT columns are allocated using overlay pages and I stumbled upon something interesting and unexpected. Let me present to you my findings, along with my attempt at explaining what is happening.

InnoDB Tablespaces

The first oddity I found is a bunch of free pages in each tablespace it is skipping. Here’s an example from a simple table with only an integer primary key and a char(32) column:

root@LabPS8_1:~/1btr# innodb_space -f /var/lib/mysql/test/t1.ibd space-extents
start_page  page_used_bitmap
0               #####################################........................... <--- free pages
64              ################################################################
128 …

As database footprints continue to explode, many companies are looking for ways to deal with such rapid growth.  One approach is to refactor traditional relational databases to fit into a NoSQL engine, where horizontal scalability is easier.  However, in many cases, this is in no way a trivial undertaking.

Another approach that has been gaining interest is the use of MyRocks as an alternative storage engine to the traditional InnoDB.  While not for everyone, in certain use cases it could be a potential solution.  As with so many things open source, the next standard questions are: which version should I use?  Any differences with the engine if I use MyRocks with MySQL 5.7 vs 8.0?

In this post, I wanted to touch on this and give some high-level thoughts on MyRocks when it comes to the version of MySQL.

…

Percona Technical Account Managers get the privilege of working with some of our largest enterprise clients day in and day out.  As such, we get to really focus on how to best leverage our technology to generate measurable benefits for our users.  While it is fun to “nerd out” and always strive to use the latest and greatest, we need to stay focused on demonstrating business value and a genuine need.  Over the past few months, I’ve been working with one of my larger clients, Dropbox, along with our professional services team to validate the use of Percona Server for MySQL with the MyRocks storage engine over a large portion of their MySQL infrastructure.

Please note – this is not meant to be a deep dive into the technical details around …

For MySQL, MyISAM and InnoDB storage engines are very popular. Currently, we are mostly using InnoDB engines for high reliability and high performance. Apart from those engines, we also have some other alternative engines and they have some nice features in them. In this blog, I am going to explain some of those engines, which I have listed below. 

• FEDERATED Storage Engine
• Merge or MRG_MyISAM Engine
• Blackhole Engine
• CSV Engine

FEDERATED Storage Engine Overview:

• FEDERATED Storage Engine allows you to access the data remotely without replication and cluster technologies. 
• Using the FEDERATED tables, you can scale your server load. Queries for the given table will be sent over the network to another MySQL instance. In this case, to scale the DB, you can use many MySQL instances without changing the application code.
• FEDERATED tables …

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 …

In this post, we will discuss what to do when you add more memory to your instance. Adding memory to a server where MySQL is running is common practice when scaling resources.

First, Some Context

Scaling resources is just adding more resources to your environment, and this can be split in two main ways: vertical scaling and horizontal scaling.

Vertical scaling is increasing hardware capacity for a given instance, thus having a more powerful server, while horizontal scaling is adding more servers, a pretty standard approach for load balancing and sharding.

As traffic grows, working datasets are getting bigger, and thus we start to suffer because the data that doesn’t fit into memory has to be retrieved from disk. This is a costly operation, even with modern NVME drives, so at some point, we will need to deal with either of the scaling solutions we mentioned.

In this case, we will discuss adding more …

Sometimes, you may experience “ERROR 1034: Incorrect key file” while running the ALTER TABLE or CREATE INDEX command:

mysql> alter table ontime add key(FlightDate);
ERROR 1034 (HY000): Incorrect key file for table 'ontime'; try to repair it

As the error message mentions key file, it is reasonable to assume we’re dealing with the MyISAM storage engine (the legacy storage engine which used to have such a thing), but no, we can clearly see this table is InnoDB!

When the error message in MySQL is confusing or otherwise unhelpful, it is a good idea to check the MySQL error log:

2019-02-24T02:02:26.100600Z 9 [Warning] [MY-012637] [InnoDB] 1048576 bytes should have been written. Only 696320 bytes written. Retrying for the remaining bytes.
2019-02-24T02:02:26.100884Z 9 [Warning] [MY-012638] [InnoDB] Retry attempts for writing partial data failed.
2019-02-24T02:02:26.100894Z 9 [ERROR] [MY-012639] [InnoDB] Write to file (merge) …

As the second part of the earlier post Give Love to Your SSDs – Reduce innodb_io_capacity_max! we wanted to put together some concepts on how InnoDB flushing works in recent Percona Server for MySQL versions (8.0.x prior to 8.0.19, or 5.7.x). It is important to understand this aspect of InnoDB in order to tune it correctly. This post is a bit long and complex as it goes very deep into some InnoDB internals.

InnoDB internally handles flush operations in the background to remove dirty pages from the buffer pool. A dirty page is a page that is modified in memory but not yet flushed to disk. This is done to lower the write load and the latency of the transactions. Let’s explore the various sources of flushing inside InnoDB.

Idle Flushing

We already discussed the idle flushing in the previous post …