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Displaying posts with tag: Insight for DBAs (reset)
MySQL 8.0.22: Asynchronous Replication Automatic Connection (IO Thread) Failover

MySQL 8.0.22 was released on Oct 19, 2020, and came with nice features and a lot of bug fixes. Now, you can configure your async replica to choose the new source in case the existing source connection (IO thread) fails. In this blog, I am going to explain the entire process involved in this configuration with a use case.

Overview

This feature is very helpful to keep your replica server in sync in case of current source fails. 

To activate asynchronous connection failover, we need to set the “SOURCE_CONNECTION_AUTO_FAILOVER=1” on the “CHANGE MASTER” statement.

Once the IO connection fails, it will try to connect the existing source based on the “MASTER_RETRY_COUNT, MASTER_CONNECT_RETRY”. Then only it will do the failover. 

The feature will only work when the IO connection is failed, maybe the source crashed or stopped, or any network failures. This will not work if the replica is …

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MySQL New Releases and Percona XtraBackup Incompatibilities

Earlier this week, Oracle released their Q4 releases series. As on the previous releases, backward compatibility has been broken with previous versions of the server. This time on both MySQL 5.7 and 8.0:

MySQL 5.7.32

While our QA team was performing an extensive test on it,  we found out this version introduced a new compression format version. This change breaks backward compatibility with older versions of MySQL, which is expected on the 8.0 series but is not on 5.7. As Percona XtraBackup (PXB) is based on MySQL code, it makes MySQL 5.7.32 incompatible with current versions of Percona XtraBackup 2.4.20 and prior.

The issue does not affect only Percona XtraBackup but also prevents users from downgrading the server from 5.7.32 to any lower version on the 5.7 series – More details at …

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Using Volume Snapshot/Clone in Kubernetes

One of the most exciting storage-related features in Kubernetes is Volume snapshot and clone. It allows you to take a snapshot of data volume and later to clone into a new volume, which opens a variety of possibilities like instant backups or testing upgrades. This feature also brings Kubernetes deployments close to cloud providers, which allow you to get volume snapshots with one click.

Word of caution: for the database, it still might be required to apply fsfreeze and FLUSH TABLES WITH READ LOCK or

LOCK BINLOG FOR BACKUP

.

It is much easier in MySQL 8 now, because as with atomic DDL, MySQL 8 should provide crash-safe consistent snapshots without additional locking.

Let’s review how we can use this feature with Google Cloud Kubernetes Engine and …

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Danger of Changing Default of log_error_verbosity on MySQL/Percona Server for MySQL 5.7

Changing the default value (3) of log_error_verbosity in MySQL/Percona Server for MySQL 5.7 can have a hidden unintended effect! What does log_error_verbosity do exactly? As per the documentation:

The log_error_verbosity system variable specifies the verbosity for handling events intended for the error log.

Basically a value of 1 logs only [Errors]; 2 is 1)+[Warnings]; and 3 is 2)+[Notes].

For example, one might be tempted to change the default of log_error_verbosity since the error.log might be bloated with thousands (or millions) of lines with [Notes], such as:

2020-10-08T17:02:56.736179Z 3 [Note] Access denied for user 'root'@'localhost' (using password: NO)
2020-10-08T17:04:48.149038Z 4 [Note] Aborted connection 4 to db: 'unconnected' user: 'root' host: 'localhost' (Got timeout reading communication packets)

(P.S. you can read more about those Notes on this other Percona blog posts):

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Dangerous Edge Case Warning for Percona Toolkit and pt-online-schema-change

Recently I was dealing with an unexpected issue raised by our Support customer, in which data became inconsistent after a schema change was applied.

After some investigation, it turned out that affected tables had a special word in the comments of some columns, which triggered an already known (and fixed) issue with the TableParser.pm library of Percona Toolkit.  The problem is that the customer was using an outdated Toolkit version, where pt-online-schema-change was using that buggy parser.

This bug applies only to Percona Toolkit versions up to 3.0.10, so if you have already 3.0.11 or newer installed, you can skip the rest of this post as these are no longer affected.

I am writing this post to warn every user of pt-online-schema-change who has not upgraded the toolkit, as …

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How to Find Query Slowdowns Using Percona Monitoring and Management

Visibility is a blessing, and with databases, visibility is a must. That’s true not only for metrics but for the queries themselves. Having info on all the stats around query execution is priceless, and Percona Monitoring and Management (PMM) offers that in the form of the Query Analytics dashboard (QAN).

But where to start? QAN helps you with that by calculating the query profile. What is the profile? It’s a rank of queries, ordered by Load, so it is easy to spot the heaviest queries hitting your database. The Load is defined as the “Average Active Queries” but can also be defined as a mix of Query Execution Time Plus Query count. In other words, all the time the query was alive and kicking.

The Profile in PMM 2.10.0 looks like this:

The purpose of this profile is to facilitate the task of finding the …

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How to Use CHECK Constraint in MySQL 8

Hello everyone, in this little post we will review a new feature in MySQL 8.

What is “CHECK Constraint”?

This is a new feature to specify a condition to check the value before INSERT or UPDATE into a row. The constraint could return an error if the result of a search condition is FALSE for any row of the table (but not if the result is UNKNOWN or TRUE).

This feature starts working on MySQL 8.0.16, and in previous versions, we could create it, but it doesn’t work, meaning the syntax is supported but it is not working,

There are some rules to keep in mind…

– AUTO_INCREMENT columns are not permitted
– Refer to another column in another table is not permitted
– Stored functions and user-defined functions are not permitted (you can not call a function or any user-defined functions)
– Stored procedure and function parameters are not permitted (you cannot call …

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Rate Limit (Throttle) for MySQL with ProxySQL

Maybe one of the more “obscure” operations when dealing with replica lag, or, in general, when one needs to control writes to the database, is the Rate limit. It’s also lately one of the most popular conversations around the community.

But what is it? In plain words: holding up queries for a while, giving air to the replicas to breath and catch up. Something similar to the Galera’s Flow Control mechanism, although flow control, when it kicks in, stops all the writes while the nodes catch up. With a throttle no write is stopped, just delayed.

There are several ways to do this. A popular tool is Freno but this is also something that can be achieved with ProxySQL. Let’s see how.

Delay

ProxySQL has a variable called …

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MySQL 101: Tuning MySQL After Upgrading Memory

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 …

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Diagnosing and Fixing “MySQL Server Has Gone Away” Messages

We all like when error messages are descriptive and give a clear idea about what is happening; however, there are some cases when a few possible reasons lay behind one error message. “MySQL server has gone away” is one of them. Most of the cases when the error occurs are described in MySQL documentation, but it can get tricky. And here, I’d like to talk about “tricky”.

There are only a few major cases when this happens:

1. MySQL Thread Was Killed by an Administrator or a Utility Such as pt-kill

The manual intervention is likely to be intermittent and, as it is a one-time thing in certain situations (e.g., a bad long-running query), probably would be known to a DBA. Pt-kill might be less noticeable, as it is often left running as a workaround to prevent those bad long queries from taxing system resources. Checking the system …

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