vmcj/nested_lock_loops 

Use

When requesting VM-wide locks ( Shared Locks), the following points must be considered:

If another lock is requested within an area protected by a shared lock, and the wrong sequence is used, a deadlock may result.

If a VM-wide garbage collection ( Shared Garbage Collection) is active, a VM that has just requested a shared lock must first contribute to the garbage collection before it can receive the shared lock. To enable this to happen, the lock request is not allowed to block.

If a timeout occurs at the first attempt to receive the lock, the VM enters a loop during which control is relinquished for a short time, and the lock request is repeated.

The number of loops can be limited with the parameter vmcj/nested_lock_loops:

Properties

Work area	VM container
Unit	Integer value
Standard value	-1
Dynamically changeable	Local and on all servers

Value Range and Syntax

The following values are permitted:

-1:Endless attempts are made to set the lock.

n>= 0: Maximum number of attempts to set the lock. Each attempt lasts for about one second. If the lock still could not be set after n number of attempts, the lock request is rejected.

SAP Recommendation

Only change the parameter if you are sure that there really is a deadlock, and then try to solve the problem.