How to unlock SYSTEM user in SAP HANA Database

SAP HANA SYSTEM user can now be locked for too many failed logon attempts.

Symptom :
            Starting from SAP HANA Revision 102, the SYSTEM user can be locked if logon attempts fail for too many times, just like the other database users. A new parameter "password_lock_for_system_user" has been introduced in section [password policy] of file indexserver.ini for this purpose. And the default locking time is 1044 minutes (1 day).

Solution :
       The new password policy for the SYSTEM user is introduced to prevent brute-force attacks to guess the password of SYSTEM and to improve the security of SAP HANA. However, in the event that the SYSTEM user is locked, any activities that are dependent on the SYSTEM user to make the database connection are affected. For example, monitoring activities and operations on the SAP HANA database become impossible within the locking period; for SAP Business One, version for SAP HANA, any new logons within the locking period are not possible if your company connects to SAP HANA using the SYSTEM user.

     Therefore, we highly recommend that you create a backup user with the "USER ADMIN" system privilege. In case of an emergency where the SYSTEM user is locked, you can use this backup user to unlock the SYSTEM user.
To unlock the SYSTEM user that was locked after (default 5 times), 

run this SQL statement: ALTER USER SYSTEM RESET CONNECT ATTEMPTS

Note:  As an alternative, you can set the "password_lock_for_system_user" value as "false" and the SYSTEM user will be excluded from the password policy. However, this is NOT recommended and should work only as a workaround

More Details refer  snote :2251556