Thank you for quick reply. Based on your comment, I understood in this way.
If my log data is like this as mentioned below
log row one: {"ORDER_TYPE":"New","COUNT_ROWS":4}
log row two: {"ORDER_TYPE":"Change","COUNT_ROWS":10}
log row two: {"ORDER_TYPE":"Delete","COUNT_ROWS":50}
in this case, COUNT_ROWS will appear under Metrics but ORDER_TYPE will not. Is this correct ?