Showing entries 11 to 20 of 24
« 10 Newer Entries | 4 Older Entries »
Displaying posts with tag: pt-online-schema-change (reset)
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 …

[Read more]
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, …

[Read more]
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 …

[Read more]
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 …

[Read more]
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 …

[Read more]
Syncing MySQL slave table with pt-online-schema-change

I recently encountered a situation in which after running Percona Toolkit’s pt-table-checksum on a customer system, 95% of the table on the MySQL master was different on the MySQL slave. Although this table was not a critical part of the infrastructure, from time to time, writes to the table from the master would break replication. Additionally, this table has about 6 million rows, and running pt-table-sync would take sometime. Rebuilding the slave from backup of the master would not be an easy option as well since the slave acts as an archive where it has a lot more data than the master.

So how did we solve it? With pt-online-schema-change and a NOOP ALTER.

pt-online-schema-change --alter 'ENGINE=INNODB' D=dbname,t=tblname

How is it …

[Read more]
Looking out for max values in integer-based columns in MySQL

Yay! My first blog post! As long as at least 1 person finds it useful, I’ve done my job. Recently, one of my long-term clients was noticing that while their INSERTs were succeeding, a particular column counter was not incrementing. A quick investigation determined the column was of type int(11) and they had reached the maximum value of 2147483647. We fixed this by using pt-online-schema-change to change the column to int(10) unsigned, thus allowing values up to 4294967295.

My client was now concerned about all his other integer-based columns and wanted me to check them all. So I wrote a quick-n-dirty script in Go to check all integer-based columns on their current value compared to the maximum allowed for that column type.

You …

[Read more]
How to monitor ALTER TABLE progress in MySQL

While working on a recent support issue as a Percona Support Engineer,  I got one question from a customer asking how to monitor ALTER TABLE progress. Actually, for MySQL 5.5 and prior versions, it’s quite difficult to ALTER the table in a running production environment especially for large tables (with millions records). Because it will rebuild and lock the table affecting the performance as well as our users. Therefore even if we start ALTER it’s really important to know when it will finish. Even while creating the index, ALTER TABLE will not rebuild the table if fast_index_creation is ON but still it might lock the table.

[Read more]
Online Schema Upgrade in MySQL Galera Cluster using TOI Method

December 10, 2013 By Severalnines

As a follow-up to the Webinar on Zero Downtime Schema Changes in Galera Cluster, we’ll now walk you through the detailed steps on how to update your schema. The two methods (TOI and RSU) have both their pros and cons, and given parameters like table size, indexes, key_buffer_size, disk speed, etc., it is possible to estimate the time taken for the schema to be upgraded. Also, please note that a schema change is non-transactional so it would not be possible to rollback the DDL if it fails midway. Therefore, it is always recommended to test the schema changes and ensure you have recoverable backups before performing this on your production clusters. 

This post examines the way DDL changes are propagated in Galera, and outlines the steps to upgrade the …

[Read more]
Integrating pt-online-schema-change with a Scripted Deployment

Recently, I helped a client that was having issues with deployments causing locking in their production databases.  At a high level, the two key components used in the environment were:

  • Capistrano (scripted deployments) [website]
  • Liquibase (database version control) [website]

At a high level, they currently used a CLI call to Liquibase as a sub-task within a larger deployment task.  The goal of this engagement was to modify that sub-task to run Liquibase in a non-blocking fashion as opposed to the default that just runs native ALTERS against the database.

As I wasn’t very familiar with Liquibase, I took this opportunity to learn more about it and it seems like a very valuable tool.  Essentially, it does the following:

  • Adds two version control tables to …
[Read more]
Showing entries 11 to 20 of 24
« 10 Newer Entries | 4 Older Entries »