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Displaying posts with tag: Insight for DBAs (reset)
Dropping Foreign Key constraint using pt-online-schema-change

Before we proceed, here is useful blog post  written by Peter on Hijacking Innodb Foreign Keys.

However, if you are trying to get rid of an unused Foreign Key (FK) constraint and related columns from versions older than mysql 5.6 or tables which cannot be executed with


  because of limitations mentioned here (specifically tables with 5.5 TIMESTAMP formats), you can use pt-online-schema-change  to drop such foreign keys.



  with  PT-OSC requires specifying


  rather than the real

constraint_name …
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Dropping the Foreign Key Constraint Using pt-online-schema-change

In this blog post, we’ll look at how to get rid of the unused Foreign Key (FK) constraint and/or related columns/keys with the help of pt-online-schema-change and the power of its plugins.

Before we proceed, here is a useful blog post written by Peter Zaitsev on Hijacking Innodb Foreign Keys.

If you are trying to get rid of an unused foreign key (FK) constraint and related columns from versions older than MySQL 5.6, or tables that cannot be executed with


 because of limitations mentioned here (specifically, …

[Read more]
Prophet: Forecasting our Metrics (or Predicting the Future)

In this blog post, we’ll look at how Prophet can forecast metrics.

Facebook recently released a forecasting tool called Prophet. Prophet can forecast a particular metric in which we have an interest. It works by fitting time-series data to get a prediction of how that metric will look in the future.

For example, it could be used to:

  • Predict how much HTTP traffic we will get, and scale accordingly when needed
  • See if a particular feature of our application will have success or if its usage will decline
  • Get an approximate date when our database server’s resources will be exhausted
  • Forecast new customer’s sign up and resize the staff accordingly
  • See what next year’s Black Friday or Cyber Monday will look like, and if we have the resources to handle them
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MySQL, –i-am-a-dummy!

In this blog post, we’ll look at how “operator error” can cause serious problems (like the one we saw last week with AWS), and how to avoid them in MySQL using



Recently, AWS had some serious downtime in their East region, which they explained as the consequence of a bad deployment. It seems like most of the Internet was affected in one way or another. Some on Twitter dubbed it “S3 Dependency Awareness Day.”

Since the outage, many companies (especially Amazon!) are reviewing their production access and deployment procedures. It would be a lie if I claimed I’ve never made a mistake in production. In fact, I would be afraid of working with someone who claims to have never made a mistake in a production environment.

Making a mistake or two is how you learn to have a full …

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Quest for Better Replication in MySQL: Galera vs. Group Replication

UPDATE: Some of the language in the original post was considered overly-critical of Oracle by some community members. This was not my intent, and I’ve modified the language to be less so. I’ve also changed term “synchronous” (which the use of is inaccurate and misleading) to “virtually synchronous.” This term is more accurate and already used by both technologies’ founders, and should be less misleading.

I also wanted to thank Jean-François Gagné for pointing out the incorrect sentence about multi-threaded slaves in Group Replication, which I also corrected accordingly.

In today’s blog post, I will briefly compare two major virtually synchronous replication technologies available today for MySQL.

More Than Asynchronous Replication

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Using NVMe Command Line Tools to Check NVMe Flash Health

In this blog post, I’ll look at the types of NVMe flash health information you can get from using the NVMe command line tools.

Checking SATA-based drive health is easy. Whether it’s an SSD or older spinning drive, you can use the


 command to get a wealth of information about the device’s performance and health. As an example:

root@blinky:/var/lib/mysql# smartctl -A /dev/sda
smartctl 6.5 2016-01-24 r4214 [x86_64-linux-4.4.0-62-generic] (local build)
Copyright (C) 2002-16, Bruce Allen, Christian Franke,
SMART Attributes Data Structure revision number: 16
Vendor Specific SMART Attributes with Thresholds:
 1 Raw_Read_Error_Rate     0x002f   100   100   000 …
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MySQL super_read_only Bugs

This blog we describe an issue with MySQL 5.7’s super_read_only feature when used alongside with GTID in chained slave instances.


In MySQL 5.7.5 and onward introduced the gtid_executed table in the MySQL database to store every GTID. This allows slave instances to use the GTID feature regardless whether the binlog option is set or not. Here is an example of the rows in the gtid_executed table:

mysql> SELECT * FROM mysql.gtid_executed;
| source_uuid                          | interval_start | interval_end | …
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WAN Synchronous Clusters: Dealing with Latency Using Concurrency

In this blog, we’ll discuss how to use concurrency to help with WAN latency when using synchronous clusters.

WAN Latency Problem

Our customers often ask us for help or advice with WAN clustering problems. Historically, the usual solution for MySQL WAN deployments is having the primary site in one data center, and stand-by backup site in another data center (replicating from the primary asynchronously). These days, however, there is a huge desire to employ available synchronous replication solutions for MySQL. These solutions include things like Galera (i.e., Percona XtraDB Cluster) or the recently released MySQL Group Replication. This trend is attributable to the fact that these solutions are less problematic and provide more automatic fail over and fail back procedures. But it’s also because businesses want to write in both data centers simultaneously.

Unfortunately, WAN link reliability and latency makes …

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MySQL Sharding Models for SaaS Applications

In this blog post, I’ll discuss MySQL sharding models, and how they apply to SaaS application environments.

MySQL is one of the most popular database technologies used to build many modern SaaS applications, ranging from simple productivity tools to business-critical applications for the financial and healthcare industries.

Pretty much any large scale SaaS application powered by MySQL uses sharding to scale. In this blog post, we will discuss sharding choices as they apply to these kinds of applications.

In MySQL, unlike in some more modern technologies such as MongoDB, there is no standard sharding implementation that the vast majority of applications …

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When MySQL Lies: Wrong seconds_behind_master with slave_parallel_workers > 0

In today’s blog, I will show an issue with seconds_behind_master that one of our clients faced when running slave_parallel_works > 0. We found out that the reported seconds_behind_master from SHOW SLAVE STATUS was lying. To be more specific, I’m talking about bugs #84415 and #1654091.

The Issue

MySQL will not report the correct slave lag if you have slave_parallel_workers> 0. Let’s show it in practice.

I’ll use MySQL Sandbox to speed up one master and two slaves on MySQL version …

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