Types of locks Modes in SAP ABAP :

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Types of locks :

We can use different type of locks.The lock mode describe what type of lock it is and the lock modes are listed in the table below:

Locks Modes:
Type of Lock
Lock mode
Description
Shared lock          
S (Shared)
Several user [transaction] can access locked data at the same time in display mode.A request for another shared lock is accepted and even if it comes from another user. So an exclusive lock set on an object that already has a shared lock will be rejected.  
Exclusive lock
E (Exclusive)
An exclusive lock protect the locked object against all type of lock from other transaction.Only the same lock owner can reset the lock [accumulate].
Exclusive but not cumulative lock
X (eXclusive non-cumulative)
Exclusive locks can be requested several time from the same transaction and are processed successively.In contrast, exclusive but not cumulative locks can be called only once from the same transaction.Each further lock request will be rejected.
Optimistic lock
O (Optimistic)
Optimistic lock initially behave like shared lock and can be converted into exclusive lock.See Optimistic Lock.


































































Lock Server & Enqueue Communication in a distributed SAP system, one lock server [also known to as the enqueue server] manage the lock table & the lock server can run on the central instance or on a standalone system.

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