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Displaying posts with tag: pt-online-schema-change (reset)
Percona Toolkit 2.2.20 is now available

Percona announces the availability of Percona Toolkit 2.2.20. Released December 9, 2016, Percona Toolkit is a collection of advanced command-line tools that perform a variety of MySQL server and system tasks that DBAs find too difficult or complex for to perform manually. Percona Toolkit, like all Percona software, is free and open source.

This release is the current GA (Generally Available) stable release in the 2.2 series. Downloads are available here and from the Percona Software Repositories.

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Changing the Tablespace Directory with pt-online-schema-change

In this blog, we’ll discuss changing the tablespace directory using pt-online-schema-change.

One of the most annoying situations in the life of a DBA is realizing that the disk where the datadir resides is running out of space. If you’re lucky enough to run over an LVM volume or a RAID (depending on the level, though), it is easy to add disk space. But what if you are not that lucky, and your datadir is running on a single disk? Not so funny!

That is the exact situation we recently faced with a customer, for both the master and slave server. When trying to figure out a solution we saw that:

  • There was enough space on a different partition within the same server.
  • The tables have their own tablespace (innodb_file_per_table = on)
  • The MySQL version was …
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Amazon RDS and pt-online-schema-change

In this blog post, I discuss some of the insights needed when using Amazon RDS and pt-online-schema-change together.

The pt-online-schema-change tool runs DDL queries (ALTER) online so that the table is not locked for reads and writes. It is a commonly used tool by community users and customers. Using it on Amazon RDS requires knowing about some specific details. First, a high-level explanation of how the tool works.

This is an example from the documentation:

pt-online-schema-change --alter "ADD COLUMN c1 INT" D=sakila,t=actor

The tool runs an ALTER on the table “actor” from the database “sakila.” The alter adds a column named “c1” of type …

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Rescuing a crashed pt-online-schema-change with pt-archiver

This article discusses how to salvage a crashed pt-online-schema-change by leveraging pt-archiver and executing queries to ensure that the data gets accurately migrated. I will show you how to continue the data copy process, and how to safely close out the pt-online-schema-change via manual operations such as RENAME TABLE and DROP TRIGGER commands. The normal process to recover from a crashed pt-online-schema-change is to drop the triggers on your original table and drop the new table created by the script. Then you would restart pt-online-schema-change. In this case, this wasn’t possible.

A customer recently needed to add a primary key column to a very busy table (with around 200 million rows). The table only had a …

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pt-online-schema-change (if misused) can’t save the day

In this blog post we’ll discuss pt-online-schema-change, and how to correctly use it.

Always use pt-osc?

Altering large tables can be still a problematic DBA task, even now after we’ve improved Online DDL features in MySQL 5.6 and 5.7. Some ALTER types are still not online, or sometimes just too expensive to execute on busy production master.

So in some cases, we may want to apply an

ALTER

 first on slaves, taking them out of traffic pool one by one and bringing them back after the

ALTER

 is done. In the end, we can promote one of the already altered slaves to be new master, so that the downtime/maintenance time is greatly minimized. The ex-master can be altered later, without affecting production. Of course, this method works best when the schema change is …

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In Depth: MySQL 5.6+ DDL

Overview

DDL (Data Definition Language) statements create, alter, and remove database objects. These types of changes can be a very dangerous action to take on such a critical piece of your infrastructure. You want to make sure that the command that you are executing has been given proper thought and testing.

In this post I go through multiple version of MySQL and verify the best course of action to take in regards to executing DDL statements.  There are many things that you have to consider when making these types of changes, such as disk space, load on the database server, slave replication, the type of DDL statement you are executing, and if it will lock the table. 

Because of these risks, there are tools that can be used to help mitigate some of the dangers. But unless you have tested and verified their functionality, these tools in themselves can cause trouble. Whenever in doubt, take the time to test …

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Testing MySQL partitioning with pt-online-schema-change

There are cases where we need to implement MySQL partitioning, or at least test if it is an option to solve an issue. However, how are we able to test it when the table on our production environment has hundreds of millions of rows, several composite indexes and/or the size on disk is hundreds of gigabytes?

Testing environments usually don’t have all the data that production has and if they have, probably you are not testing all the use-cases at a database level. Therefore, is it possible to test MySQL Partitioning on production impacting as less as possible?

When we execute pt-online-schema-change, it creates a table, triggers, and then copies the data. As we are going to test partitioning we are going to need both tables – with and without partitioning – and we are going to use triggers to keep both tables consistent. A good thing about changing a table to use partitioning is that, usually, …

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Useful queries on MySQL information_schema

MySQL information_schema comes with useful information about the database instance, status, … etc. which is needed for daily DBA work.
There are some simple queries on the information_schema that I use on my daily basis in which I’m writing this post for my reference and maybe a good reference for someone else too …

Finding tables without Primary or Unique Keys:

PKs are so important, especially, for InnoDB tables as MySQL uses PKs as a clustered index and having no PKs might lead to severe performance problems.

Also having no PKs is one of the main causes of slave lagging problems mainly when using RBR (Row-Based Replication), e.g. if a delete statement on the master will delete 1 million rows on a table without PK, a full table scan will take place. This “might” not be a problem on the master but on the slave 1 million full table scan will take place – because changes to the individual rows are being …

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Schema changes in MySQL for OpenStack Trove users

People using OpenStack Trove instances can hit a common issue in the MySQL world: how to perform schema change operations while minimizing the impact on the database server? Let’s explore the options that can allow online schema changes.

Summary

With MySQL 5.5, pt-online-schema-change from Percona Toolkit is your best option for large tables while regular ALTER TABLE statements are only acceptable for small tables. Also beware of metadata locks.

With MySQL 5.6, almost all types of schema changes can be done online. Metadata locks can also be an issue. pt-online-schema-change can still be worth using as it is also online on read replicas.

Regular ALTER TABLE with MySQL 5.5

If you are still using MySQL 5.5, almost all schema changes will require a table …

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Avoiding MySQL ALTER table downtime

MySQL table alterations can interrupt production traffic causing bad customer experience or in worst cases, loss of revenue. Not all DBAs, developers, syadmins know MySQL well enough to avoid this pitfall. DBAs usually encounter these kinds of production interruptions when working with upgrade scripts that touch both application and database or if an inexperienced admin/dev engineer perform the schema change without knowing how MySQL operates internally.

Truths
* Direct MySQL ALTER table locks for duration of change (pre-5.6)
* Online DDL in MySQL 5.6 is not always online and may incurr locks
* Even with Percona Toolkit‘s pt-online-schema-change there are several workloads that can experience blocking

Here on the Percona MySQL …

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