redmine/db/migrate/20161010081600_change_journals_notes_limit.rb

class ChangeJournalsNotesLimit < ActiveRecord::Migration[4.2]
  def up
    if ActiveRecord::Base.connection.adapter_name =~ /mysql/i
      max_size = 16.megabytes
      change_column :journals, :notes, :text, :limit => max_size
    end
  end

  def down
    # no-op
  end
end