MySQL 8.0.13 improves replication lag monitoring by extending the instrumentation for transaction transient errors. These temporary errors, which include lock timeouts caused by client transactions executing concurrently as the slave is replicating, do not stop the applier thread: instead, they cause a transaction to retry.…

Parallel replication has been around for a few years now but is still not that commonly used. I had a customer where the master had a very large write workload. The slave could not keep up so I recommended to use parallel slave threads. But how can I measure if it really helps and is working?

At my customer the

slave_parallel_workers

  was 0. But how big should I increase it, maybe to 1? Maybe to 10? There is a blog post about how can we see how many threads are actually used, which is a great help.

We changed the following variables on the slave:

slave_parallel_type = LOGICAL_CLOCK;
slave_parallel_workers = 40;
slave_preserve_commit_order = ON;

40 threads sounds a lot, right? Of course, this is workload specific: if the transactions are independent it might be …

Probably not well known but quite an important optimization was introduced in MySQL 5.6 – reduced overhead for “read only transactions”. While usually by a “transaction” we mean a query or a group of queries that change data, with transaction engines like InnoDB, every data read or write operation is a transaction.

Now, as a non-locking read operation obviously has less impact on the data, it does not need all the instrumenting overhead a write transaction has. The main thing that can be avoided, as described by documentation, is the transaction ID. So, since MySQL 5.6, a read only transaction does not have a transaction ID. Moreover, such a transaction is not visible in the SHOW ENGINE INNODB STATUS output, though I will not go deeper on what really that means under the hood in this article. The fact is that this optimization …

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Since MySQL 5.6, the digest feature of the MySQL Performance Schema has provided a convenient and effective way to obtain statistics of queries based on their normalized form. The feature works so well that it has almost completely (from my experience) replaced the connector extensions and proxy for collecting query statistics for the Query Analyzer (Quan) in MySQL Enterprise Monitor (MEM).

MySQL 8 adds further improvements to the digest feature in the Performance Schema including a sample query with statistics for each digest, percentile information, and a histogram summary. This blog will explore these new features.

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The traditional way to monitor replication in MySQL is the SHOW SLAVE STATUS command. However as it will be shown, it has its limitations and in MySQL 5.7 and 8.0 the MySQL developers have started to implement the information as Performance Schema tables. This has several advantages including better monitoring of the replication delay in MySQL 8.0. This blog discusses why SHOW SLAVE STATUS should be replaced with the Performance Schema tables.

The Setup

The replication setup that will be used for the examples in this blog can be seen in the following figure.

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The Performance Schema and sys schema are great for investigating what is going on in MySQL including investigating performance issues. In my work in MySQL Support, I have a several times heard questions whether a peak in the InnoDB Data File I/O – Latency graph in MySQL Enterprise Monitor (MEM) or some values from the corresponding tables and view in the Performance Schema and sys schema are cause for concern. This blog will discuss what these observations means and how to use them.

The Tables and Views Involved

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Please join Percona’s Principal Support Escalation Specialist Sveta Smirnova as she presents Troubleshooting Best Practices: Monitoring the Production Database Without Killing Performance on Wednesday, June 27th at 11:00 AM PDT (UTC-7) / 2:00 PM EDT (UTC-4).

Register Now

During the MySQL Troubleshooting webinar series, I covered many monitoring and logging tools such as:

• General, slow, audit, binary, error log files
• Performance Schema
• Information Schema
• System …

In this blog, I will provide answers to the Q & A for the Performance Schema for MySQL Troubleshooting webinar.

First, I want to thank everybody for attending my March 1, 2018, webinar. The recording and slides for the webinar are available here. Below is the list of your questions that I was unable to answer fully during the webinar.

Q: Is Workbench able to take advantage of the enhancements to Perf schema?

A: MySQL Workbench is a graphical tool for database …

In this blog, I will provide answers to the Q & A for the Basic Internal Troubleshooting Tools for MySQL Server webinar.

First, I want to thank everybody for attending my February 15, 2018, webinar on troubleshooting tools for MySQL. The recording and slides for the webinar are available here. Below is the list of your questions that I was unable to answer fully during the webinar.

Q: How do we prevent the schema prefix from appearing in the show create view. This is causing issue with restore on another server with a different DB. See the issue …

Please join Percona’s Principal Support Engineer, Sveta Smirnova, as she presents Performance Schema for MySQL Troubleshooting on Thursday, March 1, 2018, at 10:00 am PST (UTC-8) / 1:00 pm EST (UTC-5).

Register Now

Performance Schema, first introduced in version 5.5, is a really powerful tool. It is actively under development, and each new version provides even more instruments for database administrators.

Performance Schema is complicated. It is also not free: it can slow down performance if you enable certain …