Class: OnlineMigrations::BackgroundDataMigrations::Scheduler

Inherits:
Object
  • Object
show all
Defined in:
lib/online_migrations/background_data_migrations/scheduler.rb

Overview

Class responsible for scheduling background data migrations.

Scheduler should be configured to run periodically, for example, via cron.

Examples:

Run via whenever

# add this to schedule.rb
every 1.minute do
  runner "OnlineMigrations.run_background_data_migrations"
end

Specific shard

every 1.minute do
  runner "OnlineMigrations.run_background_data_migrations(shard: :shard_two)"
end

Custom concurrency

every 1.minute do
  # Allow to run 2 data migrations in parallel.
  runner "OnlineMigrations.run_background_data_migrations(concurrency: 2)"
end

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.run(**options) ⇒ Object 



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# File 'lib/online_migrations/background_data_migrations/scheduler.rb', line 27

def self.run(**options)
  new.run(**options)
end

Instance Method Details

#run(shard: nil, concurrency: 1) ⇒ Object

Runs Scheduler



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# File 'lib/online_migrations/background_data_migrations/scheduler.rb', line 32

def run(shard: nil, concurrency: 1)
  relation = Migration.queue_order
  relation = relation.where(shard: shard) if shard

  migrations_to_enqueue = []

  with_lock do
    stuck_migrations, active_migrations = relation.running.partition(&:stuck?)
    runnable_migrations = migrations_with_existing_classes(relation.pending) + stuck_migrations

    # Ensure no more than 'concurrency' migrations are running at the same time.
    remaining_to_enqueue = concurrency - active_migrations.count
    if remaining_to_enqueue > 0
      runnable_migrations.take(remaining_to_enqueue).each do |migration|
        migration.update!(status: :enqueued)

        migrations_to_enqueue << migration
      end
    end
  end

  migrations_to_enqueue.each do |migration|
    enqueue_migration(migration)
  end

  true
end