adjust_twitter_id_to_unsigned_bigint.rb

# If you really want safety from Twitter blowing up, this will get you
# to 18,446,744,073,709,551,615 tweets. (Remember, mediumint is smaller
# than int.) (http://dev.mysql.com/doc/refman/4.1/en/numeric-types.html)
class AdjustTwitterIdToUnsignedBigint < ActiveRecord::Migration
  def self.up
    change_column :twitter_messages, :twitter_id, "bigint unsigned"
  end

  def self.down
    change_column :twitter_messages, :twitter_id, :integer
  end
end

adjust_twitter_id_to_unsigned_int.rb

# This will get you to about 4.3 billion tweets
# (http://dev.mysql.com/doc/refman/4.1/en/numeric-types.html)
class AdjustTwitterIdToUnsignedInt < ActiveRecord::Migration
  def self.up
    change_column :twitter_messages, :twitter_id, "integer unsigned"
  end

  def self.down
    change_column :twitter_messages, :twitter_id, :integer
  end
end