code: public LogSeqNum logLogicalAbort(long txNum, LogSeqNum undoNextLSN) {
  		if (enableLogging) {
  			return new LogicalAbortRecord(txNum, undoNextLSN).writeToLog();
  		} else
  			return null;
  	}
docs: Writes a logical abort record into the log.
  
  @param txNum
  the number of aborted transaction
  @param undoNextLSN
  the LSN which the redo the Abort record should jump to
  
  @return the LSN of the log record, or null if recovery manager turns off
  the logging