What is database locks?
The database lock exists only for the duration of the database LUW, in
which the changes made in the SAP system are actually updated. Logical SAP
locks must be set in dialog programs to prevent concurrent data accesses
because set database locks may be implicitly removed before the changes have
been made to the data
Life-Span of SAP Locks or Duration of SAP Locks
Locks remains set until you either call the corresponding
DEQUEUE function module, or close the transaction with an implicit DEQUEUE_ALL.
Saved locks inherited by the update task are loaded back into the lock table
when the system is started up. Lock operations last for a few 100 microseconds
in work processes in the lock server.
Where is the lock table
stored?
In the main memory and shared memory of the enqueue server. All work processes in the enqueue server have access to it.
Can locks exist directly after
startup?
Yes, the saved locks, which were inherited by the update
task, are reloaded to the lock table during
startup.
Are
the locks in the lock table also set at the database
level?
Locks are not set on the database. The lock table is stored
in the main memory of the enqueue server.
Is a lock table built if an enqueue work process is
not started on the enqueue server in the instance
profile?
Yes, because the work processes on the enqueue server use
the lock table directly, and not via the enqueue process. The latter is only
responsible for lock requests from external application servers.
How can I find out who is currently holding the
ungranted lock? In other words, how can check the program after an ENQUEUE to
determine which use is currently holding the lock so that I can let him or her
know?
When the ENQUEUE_Name function module is returned, the name
of the lock owner is listed in SY-MSGV1.
What is Wild Cards in sap locks?
You can use special characters in your lock argument
(especially the ‘at’ sign (@)). The ‘at’ symbol is used as a wildcard in SAP
locks (enqueues). In other words, it can stand for any other character during
collision checks. In order to prevent the wildcard mechanism from being
activated in SAP locks when it is not required, you need to ensure when enqueue
function modules are called that key value parameters do not contain any
wildcard characters. If key values that you want to use to lock individual
entities do contain wildcard characters, you have to replace the wildcards with
different characters before the enqueue is called.
Can I use special characters in my lock argument
(especially the ‘at’ sign (@))?
The ‘at’ symbol is used as a wildcard in SAP locks
(enqueues). In other words, it can stand for any other character during
collision checks. For example, the parameter value 12345@ locks the quantities
123450 to 123459, 12345a to 12345z, and 12345A to 12345Z, and all other values
with any special character in the 6th character
position.
What happens to locks when the enqueue
server is restarted?
If they have not been saved to disk in the backup file, they will be
lost. The locks that are inherited by the update task when COMMIT WORK is executed after CALL FUNCTION.. IN UPDATE TASK are saved to disk. The locks are saved to disk when the update request
becomes valid, that is, with the COMMIT WORK. Each time the enqueue server is restarted, the lock entries saved on the
disk are reloaded to the lock table. A lock is saved to disk at the point at which the backup flag is set.
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