# Migration Timeouts

Migration Timeouts is a Ruby gem that adds timeouts, explicitly or implicitly, to ActiveRecord migrations.

A **lock_timeout** sets a timeout on how long PostgreSQL will wait to acquire a lock on tables being altered before failing and rolling back. This prevents lock contention, and long-running migrations.

A **statement_timeout** sets timeout on how long a single DB statement can run. If a badly constructed migration tries to lock a table for too long, this will fail the migration and trigger a rollback.

This gem provides config options for app-wide settings, and class methods for specifying or disabling timeouts for a single migration.

Migration Timeouts currently only supports [PostgreSQL](https://www.postgresql.org/)

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'migration_timeouts'
```

## Usage

Configure the default lock timeout in a Rails initializer

```ruby
#config/initializers/migration_timeouts.rb

MigrationTimeouts.configure do |config|
  config.default_lock_timeout = 3.seconds
  config.default_statement_timeout = 5.seconds
end
```

And that's all! Now every `up` migration will execute
```psql
SET LOCAL statement_timeout = 5000;
SET LOCAL lock_timeout = 3000;
```
inside the migration transaction before your migration code runs. No lock
timeout will be used for the `down` migration.

## Disabling

If you set app-wide timeout settings, you can disable them for single migrations.

Here are the available helper methods:
```ruby
  class AddFoo < ActiveRecord::Migration

    disable_lock_timeout!
    disable_statement_timeout!
    disable_timeouts!

    def change
      create_table :foo do |t|
        t.timestamps
      end
    end
  end
```

## Custom lock timeout

You can change the duration of the timeouts by using:
```ruby
  class AddBar < ActiveRecord::Migration

    lock_timeout 10.seconds
    statement_timeout 15.seconds

    def change
      create_table :bar do |t|
        t.timestamps
      end
    end
  end
```
Additionally, if you have not set app-wide timeouts, you can use this to
set a timeout for a particular migration.

## disable_ddl_transaction!

If you use `disable_ddl_transaction!`, no timeouts will occur
```ruby
  class AddMonkey < ActiveRecord::Migration

    disable_ddl_transaction!

    def change
      create_table :monkey do |t|
        t.timestamps
      end
    end
  end
```

## Thanks and alternatives
Originally forked from https://github.com/procore/migration-lock-timeout :heart: