Gh-ost: GitHub’s online schema migration tool for MySQL

Today we are announcing the open source release of gh-ost: GitHub’s triggerless online schema migration tool for MySQL.

gh-ost has been developed at GitHub in recent months to answer a problem we faced with ongoing, continuous production changes requiring modifications to MySQL tables. gh-ost changes the existing online table migration paradigm by providing a low impact, controllable, auditable, operations friendly solution.

MySQL table migration is a well known problem, and has been addressed by online schema change tools since 2009. Growing, fast-paced products often require changes to database structure. Adding/changing/removing columns and indexes etc., are blocking operations with the default MySQL behavior. We conduct such schema changes multiple times per day and wish to minimize user facing impact.

Before illustrating gh-ost, let’s address the existing solutions and the reasoning for embarking on a new tool.

Online schema migrations, existing landscape

Today, online schema changes are made possible via these three main options:

Other options include Rolling


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