Deleting a large batch of session records can really overload the DB (at least MySQL). This script paces it out a bit.

active_record_sessions_batch_delete.rb

def batch_session_prune(keep_after = 1.month.ago, batch_by = 1.day, pause_time = 10)
  time = ActiveRecord::SessionStore::Session.order(:updated_at).first[:updated_at]

  while time < keep_after
    time = time + batch_by
  
    puts "Deleting sessions from #{time.to_s(:short)}"
    ActiveRecord::SessionStore::Session.where('updated_at < ?', time).delete_all

    sleep pause_time
  end
end