pt-online-schema-change is an effective way to make database changes online, with minimal disruption to the applications that connect to the database.
In this post, we will explain what exactly pt-online-schema-change is, and how it can be used to facilitate database changes without affecting the applications connected ot the database.
What is pt-online-schema-change?
pt-online-schema-change is a tool in the Percona Toolkit, a collection of open source tools to make database administration easier. It was designed to automate the process of making database schema migrations online.
With pt-online-schema-change, you can alter tables with minimal disruption to the applications connected to the database. It works by creating an empty copy of the original table, and then replicating the data from the original table to the new one according to the schema changes.
The process works by streaming the data from the original table, applying the new schema, and finally swapping the tables when replication is complete. This way, applications can continue to run normally during the migration process, with minimal to no downtime.
How to Use pt-online-schema-change
Using pt-online-schema-change is relatively easy, though you should make sure to read the manual to familiarize yourself with the syntax and parameters. Here are the basic steps:
- Install the Percona Toolkit.
- Back up your database. Make sure to use a database backup tool such as Percona XtraBackup to avoid any data loss.
- Run the pt-online-schema-change command, specifying the database name, table, user, and password.
- Monitor the migration process, paying close attention to replication lag.
What are the prerequisites for running pt-online-schema-change?
In order to use pt-online-schema-change, you need an installed version of the Percona Toolkit. You will also need a valid database user with permissions to create and drop tables, as well as appropriate privileges to insert and update data.
How long does the process take?
The duration of the migration process depends on the number of rows and columns, the size of the database, and the speed of the server. In general, it can take anywhere from a few minutes to a few hours. In any case, keep a close eye on the replication lag, and make sure it's not getting too large.
Can I use pt-online-schema-change to add columns to a table?
Yes, it is possible to use pt-online-schema-change to add columns to an existing table. However, take into account that the new columns will have the default values specified in the schema change.
Does pt-online-schema-change support databases other than MySQL?
Currently, pt-online-schema-change only works with MySQL databases. For other databases, you will need to use alternative methods.
What happens if the migration process is interrupted?
In the event of an interruption, the migration process will be rolled back. The tables will be automatically dropped, and your database will be left in its original state.