You can see these queues with an enqueues dump at level 3. The syntax is
alter session set events 'immediate trace name enqueues level 3';
Level 1 just dumps the enqueue hash table; level 2 includes the resources; and
level 3 includes the locks and thus shows the queues. The lengths of the queues
are a function of the locking activity against the resources. The only instance
wide limits apply to the number of resources and locks in the respective fixed
arrays. These are set by the enqueue_resources and _enqueue_locks parameters respectively. Check the MAX_UTILIZATION and LIMIT_VALUE in V$RESOURCE_LIMIT to
see if you are in danger of hitting either limit.
Note 102925.1 says:
When access is required by a session, a lock structure is obtained and a request is made to acquire access to the resource at a specific level (mode) is made. The lock structure is placed on one of three linked lists which hang off of the resource, called the OWNER (if the enqueue could be acquired), WAITER (if the session is waiting to acquiring the enqueue) and CONVERTER (the session is holding the enqueue in one level but wants to convert it to another) lists.
How can I see OWNER, WAITER and CONVERTER queues, and which parameters determine the length of these queues?