Frequently Asked Questions: Lock Concept - Architecture

Question

Where is the lock table stored?                                        

Answer

In the main memory, shared memory, of the Enqueue Server. All work processes in the enqueue server have access to it. External application servers execute their lock operations in the enqueue process on the enqueue server. Communication in this case takes place via the relevant dispatchers and the message server. 

Question

Can locks exist directly after startup?              

Answer

Yes, the saved locks, which were inherited by the update task, are reloaded to the lock table during startup (see first question).       

      

Question

Why is an enqueue work process required in a central system? Don't all work processes have the same access to the shared memory and thus to the lock table?     

Answer

Although the enqueue process is not used in a central system, it does not do any harm. Since almost all customers install an application server sooner or later, problems will inevitably arise if the enqueue process is missing. For this reason, the enqueue diagnosis function will output an error if an enqueue process has not been configured.                    

       

Question

Are the locks in the lock table also set at the database level? If not, database functions could be used to process objects locked in the SAP system.                                        

Answer

Locks are not set on the database. The lock table is stored in the main memory of the enqueue server. 

                          

Question

Is a lock table built if an enqueue work process is not started on the enqueue server in the instance profile?           

Answer

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.