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