DB lock

2 types


1. Implicit locks: oracle automatically locks the rows whenever user performs DML operations.

2. Explicit locks: provided by user.



 2 tpyes 


a) Row level locks: used to lock selected rows of table. It is imposed by "for update" clause in select.

b) Table level locks: used to lock compleate table. 

3 models 


1) share mode

2) share update

3) exlcusive mode