Tip1. DB lock and avoid DB lock

1. When DB lock is occurred
   1. More than two sessions is trying to update, insert or delete same rows of data, DBMS does not decide which session is right or first-going session. Thus sessions just lock target rows of data each others and system looks stop.
2. How to AVOID DB lock
   1. Design db objects( e.g. jobbed procedures, triggers ) do not approach same set of data
   2. If two more session approach to same set of data, using db sequences when select data.
      1. db sequence only go forward by defined interval. It can make that two more session select same rows of data.

Tip2. What is SYNONYM