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The SAP System is equipped with a special lock mechanism that synchronizes access to data on the database. The purpose of the lock mechanism is to prevent two transactions from changing the same data on the database simultaneously. Lock entries are usually set and deleted automatically when user programs access a data object & release it again. The lock mechanism is closely related to the Update Mechanism.

1. You can use SM12 to check and delete lock entries.

2. In SM12, check any lock entry older > 2 days. If any outdated entry found, check the corresponding user is user online/offline in AL08 or SM04 (you can get the transaction code that been use by the user). Get the user contact from SU01 and inform about the lock else if the user is offline, release the table from lock by deleting the lock.

Note

Important profile parameters for the lock concept:-

• enque/table_size – Size of the lock table managed by the enqueue server in the main memory. The lock table contains information on which locks are currently held by whom. You can check whether the update server is functioning correctly, since the lock table can grow very fast if the update function stops. If no update problems exist, you can use this parameter to increase the size of the lock table. Default value: 4096Kb

• rdisp/wp_no_enq – Number of enqueue work processes that are to run on this instance.

• rdisp/enqname – Name of the application server that provides the enqueue service.

The lock mode:-

• Shared Lock (S) – Several users can access locked data at the same time in display mode. Requests from further shared locks are accepted, even if they are from different users. An exclusive lock set on an object that already has a shared lock will be rejected.

• Exclusive (E) – An exclusive lock protects the locked object against all types of locks from other transactions. Only the same lock owner can reset the lock .

Source: http://itsiti.com/sm12-lock-concept

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