code: public void logStatistics() {
      LOG.info("Transaction Statistics: write pointer = " + lastWritePointer +
                 ", invalid = " + invalid.size() +
                 ", in progress = " + inProgress.size() +
                 ", committing = " + committingChangeSets.size() +
                 ", committed = " + committedChangeSets.size());
    }
docs: Called from the tx service every 10 seconds.
  This hack is needed because current metrics system is not flexible when it comes to adding new metrics.