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 Locks 

The database system allows concurrent transactions to use the same database objects. Locks are required to guarantee that the parallel processes are synchronized and individual transactions isolated.

·        Among other things, the lock behavior of the database depends on the type of lock.

·        Locks can be placed on rows, tables, or the entire database catalog.

If a transaction requests too many row locks in a table, then the database system attempts to place a table lock. If this causes conflicts with other locks, the database system continues to request row locks. The limit beyond which the database system attempts to transform row locks into table locks depends on the general database parameter MAXLOCKS.

·        Locks can be requested or released either implicitly or explicitly.

The more locks that are set, and the longer these stay in place, the lower the degree of parallelism possible in the database. For this reason, make sure that locks are only set if they are absolutely necessary, and that set locks are released as soon as possible.

·        You can use the special database parameter REQUEST_TIMEOUT to restrict the amount of time that a user waits for a lock to be released.

Displaying Locks and Lock Requests

You can use, for example, the Database Manager GUI, to display information on current locks and lock requests.

Database Manager GUI, Displaying Database Activities

In SAP systems, you use the Database Assistant to display database information, or the liveCache Assistant for liveCache instances.

The system table LOCKS also contains lock information.

 

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