doytsujin / ghostferry

The swiss army knife of live data migrations

Ghostferry

Ghostferry is a library that enables you to selectively copy data from one mysql instance to another with minimal amount of downtime.

It is inspired by Github's gh-ost, although instead of copying data from and to the same database, Ghostferry copies data from one database to another and have the ability to only partially copy data.

There is an example application called ghostferry-copydb included (under the copydb directory) that demonstrates this library by copying an entire database from one machine to another.

Talk to us on IRC at irc.freenode.net #ghostferry.

• Tutorial and General Documentations: https://shopify.github.io/ghostferry
• Code documentations: https://godoc.org/github.com/Shopify/ghostferry

Overview of How it Works

An overview of Ghostferry's high-level design is expressed in the TLA+ specification, under the tlaplus directory. It maybe good to consult with that as it has a concise definition. However, the specification might not be entirely correct as proofs remain elusive.

On a high-level, Ghostferry is broken into several components, enabling it to copy data. This is documented at https://shopify.github.io/ghostferry/master/technicaloverview.html

Development Setup

Install:

• Have Docker installed
• Clone the repo
• docker-compose up -d mysql-1 mysql-2

Run tests:

• make test

Test copydb:

• make copydb && ghostferry-copydb -verbose examples/copydb/conf.json
• For a more detailed tutorial, see the documentation.

Ruby Integration Tests

Kindly take note of following options:

• DEBUG=1: To see more detailed debug output by Ghostferry
• TESTOPTS=...: As detailed under https://docs.ruby-lang.org/en/2.1.0/Rake/TestTask.html

Example: bundle exec rake test DEBUG=1 TESTOPTS="-v --name=TrivialIntegrationTests#test_logged_query_omits_columns"