Log a stack trace for every transaction... action. Only for Mysql2adapter, could be fixed to work for others.

transaction_screamer.rb

module TransactionScreamer
  def begin_db_transaction
    Rails.logger.debug "DB TRANSACTION STARTS"
    Rails.logger.debug caller.join("\n")
    super
  end

  def commit_db_transaction
    Rails.logger.debug "DB TRANSACTION ENDS"
    Rails.logger.debug caller.join("\n")
    super
  end

  def rollback_db_transaction
    Rails.logger.debug "DB TRANSACTION ROLLBACK"
    Rails.logger.debug caller.join("\n")
    super
  end
end

# uncomment the following line to see stack traces every time a transaction
# starts, is committed, or rolls back
ActiveRecord::ConnectionAdapters::Mysql2Adapter.send :prepend, TransactionScreamer