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Resolving the MySQL Active-Active Replication Dilemma

Multi-writer replication has been a challenge in the MySQL ecosystem for years before truly dedicated solutions were introduced – first Galera (and so Percona XtradDB Cluster (PXC)) replication (around 2011), and then Group Replication (first GA in 2016).

Now, with both multi-writer technologies available, do we still need traditional asynchronous replication, set up in active-active topology? Apparently yes, there are still valid use cases. And you may need it not only when for some reason Galera/PXC or GR are not suitable, but also when you actually use them. Of course, the most typical case is to have a second cluster in a different …

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Yearly Reminder: DDLs That Fail to Propagate May Cause Percona XtraDB Cluster Inconsistencies

Apologies for the silly title, but the issue is a real one, even though it is not a new thing. Schema upgrades are not an ordinary operation in Galera. For the subject at hand, the bottom line is: under the default Total Order Isolation (TOI) method, “the cluster replicates the schema change query as a statement before its execution.” What this means in practice is that a DDL issued in one node is replicated to other nodes in the cluster before it is even executed in the source node, let alone completed successfully.

As a result of this, it may fail in one node and be successful in another, and this without raising loud alerts or stopping nodes to protect against data inconsistency. This is not a bug in itself but rather a compromise of design. With new changes in MySQL and the …

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MySQL Group Replication: Conversion of GR Member to Async Replica (and Back) In the Same Cluster

MySQL Group Replication is a plugin that helps to implement highly available fault-tolerant replication topologies. In this blog, I am going to explain the complete steps involved in the below two topics.

  • How to convert the group replication member to an asynchronous replica
  • How to convert the asynchronous replica to a group replication member

Why Am I Converting From GR Back to Old Async?

Recently I had a requirement from one of our customers running 5 node GR clusters. Once a month they are doing the bulk read job for generating the business reports. When they are doing the job, it affects the overall cluster performance because of the flow control issues. The node which is executing the read job is overloaded and delays the certification and writes apply process. The read job queries can’t be split across the cluster.  So, they don’t want that …

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Replay the Execution of MySQL With RR (Record and Replay)

Chasing bugs can be a tedious task, and multi-threaded software doesn’t make it any easier. Threads will be scheduled at different times, instructions will not have deterministic results, and in order for one to reproduce a particular issue, it might require the exact same threads, doing the exact same work, at the exact same time. As you can imagine, this is not straightforward.

Let’s say your database is crashing or even having a transient stall.  By the time you get to it, the crash has happened and you are stuck restoring service quickly and doing after-the-fact forensics.  Wouldn’t it be nice to replay the work from right before or during the crash and see exactly what was happening?

Record and Replay is a technique where we record the execution of a program allowing it to be replayed over and over producing the same result. Engineers at …

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Overview of MySQL Alternative Storage Engines

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 …
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The Steps Involved in Creating a Percona Product Release

Have you ever wondered what it takes to complete Percona Server for MySQL (PS), Percona XtraDB Cluster (PXC), and Percona XtraBackup (PXB) releases? 

Let’s step back just a minute and talk about what Percona stands for. We believe we “stand on the shoulders of giants.” This means we respect our upstream sources and work to add value to the base products. Over time, new functionality is added. Much of this value-add was implemented on the 5.7 series and pulled forward to the 8.0 series. Each time we receive an upstream release, we must reapply these features to the release we receive. This process is what we call the Merge Process. …

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Is a Session Analyzer a Good Tool to Simulate Real Traffic?

Starting a long time ago, we wanted to reproduce workload in a non-production environment, and there were different attempts to achieve that goal (Query Playback is just one of them). But there is another point of view, where you need to write your own workload to do so.

Both Have Pros and Cons

Reproduce Workload:

Pros:

  • Simple to implement
  • Ready to go

Cons:

  • Need to rebuild the environment each time

Custom Scripts:

Pros:

  • Possible to have a more realistic workload
  • You can reuse the environment
  • You can use Sysbench that allows you to change …
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Low Value in range_optimizer_max_mem_size Might Cause Full Table Scan

Although how range_optimizer_max_mem_size operates is explained in the official doc, it’s not a well-known variable and surely not a variable you need to modify under most circumstances. But from time to time we get some performance tickets related to this.

What problem does this variable cause if it is not properly sized? Let’s find out with an example!

Given the following table definition:

CREATE TABLE `joinit` (
  `i` int(11) NOT NULL AUTO_INCREMENT,
  `s` varchar(64) DEFAULT NULL,
  `t` time NOT NULL,
  `g` int(11) NOT NULL,
  PRIMARY KEY (`i`)
) ENGINE=InnoDB AUTO_INCREMENT=2490316 DEFAULT CHARSET=latin1

With ~2M rows

select count(*) from joinit ;
+----------+
| count(*) |
+----------+
|  2097152 |
+----------+

With the default value of  range_optimizer_max_mem_size = 8388608, the …

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MySQL 8.0.22: SHOW PROCESSLIST Version 2 – Now Available From PERFORMANCE_SCHEMA

The “SHOW PROCESSLIST” command is very famous and very useful for MySQL DBAs. It will help you to understand the ongoing thread activities and their current states. By default, the “show processlist” output details will be collected from the thread manager, and it needs the global mutex. From MySQL 8.0.22, we have an alternative way to get the process details from the PERFORMANCE_SCHEMA. It doesn’t need the global mutex. 🙂

Note: We also have the non-blocking SYS schema views “processlist” and “x$processlist”, which provide more complete information than the SHOW PROCESSLIST statement and the INFORMATION_SCHEMA.PROCESSLIST and PERFORMANCE_SCHEMA.PROCESSLIST. But, we can’t integrate this with the “SHOW PROCESSLIST” command.

In this blog, I am going to explain the complete details about the new processlist implementation using PERFORMANCE_SCHEMA.

“SHOW PROCESSLIST” Using Thread …

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Updated MySQL OSMetrics Plugins

It has been some time since I have posted updates to my plugins.  After the initial version, I decided to split the plugins into categories of metrics.  This will allow users to choose whether they want to install all of the plugins or only select ones they care about.

Since the installation process is unfamiliar to many users, I also expanded the instructions to make it a little easier to follow.  Moreover, I added a Makefile.

I have also reformatted the output of some plugins to be either horizontal or vertical in orientation.  There is still more work to do in this area as well.

Where to Get The MySQL Plugins

You can get the plugins from GitHub at https://github.com/toritejutsu/osmetrics but they will have to be compiled from source.  As mentioned above, you can choose whether to install all of them or one by …

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