Which Three Resources Use Global Concurrency Control in 19c RAC?

Why the Answer Is Correct

Global concurrency control in a multi-instance Oracle 19c RAC database is the set of mechanisms that serialize access to resources shared by more than one instance, and the three resources named here are database block buffers, redo log buffers, and enqueues. Database block buffers are coordinated by the Global Cache Service (GCS) through cache fusion, which ships current and CR images of blocks between the buffer caches of the instances, so option A must be on the list. Enqueues are coordinated by the Global Enqueue Service (GES), which maintains the global resource directory and lets instances acquire, convert, and release enqueues cluster-wide, making option E correct. Redo log buffers complete the required trio, since redo generation and the buffer holding redo entries are managed with global concurrency control in a multi-instance database. Latches and mutexes sit outside this list precisely because they were designed only for structures touched by processes inside one instance.

Why the Other Options Are Wrong

Mutexes (B) and latches (D) are the classic intra-instance concurrency mechanisms: they are lightweight, held for very short durations, and protect memory structures that only processes of the same instance can access, so they cannot coordinate access across instances in a RAC database. Commenter jowe quotes the documentation's point that latches and mutexes "may only protect access to memory structures" reached by local processes, which is exactly why they are distractors here. JVarelaC makes the same conceptual point from the RAC course guide, noting that latches, mutexes, and enqueues are described as single-instance concurrency control before the guide moves on to RAC's additional global mechanisms. Choosing B or D therefore confuses a local serialization primitive with a cluster-wide resource, and no option other than A, C, and E can supply the three resources the question demands.

Community Comment Notes

The learner votes concentrate heavily on the three-resource set shown here, while the source key of AE supplies only two letters for a question that explicitly asks for three. jowe argues for the enqueue-centric answer and cites the rule that "latches and mutexes may only protect access to memory structures" local to one instance, which rules out B and D. JVarelaC states plainly that the proposed answer is a conceptual error because mutexes and latches are intra-instance mechanisms and the question is about global concurrency control. TrinhLK links to a RAC process reference and observes that "many resources, such as data blocks and enqueues, are used simultaneously", supporting A and E, and wiprooracle likewise reasons from global concurrency control toward an A/E-based triplet. Taking the option set and the stated "Choose three" requirement together, the only defensible completion is A, C, E.