Question 1: What is gcs_resources ?
Answer 1:
gcs_resources is global cache resources which are essentially structures we use to protect cache structures (buffers). Each instance "masters" cache resources and the implementation of this mastership is done via a gc resource structure
Question 2: What happens if it exceeds its limit?
Answer 2 :
Nothing - this is simply stating how high the value has reached for a particular resource. If we need more gcs_resources for some reason, they are obtained from the shared pool.
Question 3: How do we adjust the limit?
Answer 3 :
RAC specific memory is allocated at the time of SGA creation, mostly in the shared pool. However, the memory does not count in the SHARED_POOL_SIZE as defined in the init.ora parameter file.Therefore, when migrating Oracle from single instance to RAC, you do not need to adjust the SHARED_POOL_SIZE parameter to accommodate the additional memory that RAC uses; Oracle does that automatically. Note that the memory for the KCL global cache lock elements will be allocated in the buffer cache, and not in the shared pool.
You can monitor the exact RAC memory resource usage of the shared pool by querying V$SGASTAT for GCS, GES and KCL related entries. Also, the current and maximum number of GCS resources / shadows (resource names gcs_resources and gcs_shadows) and GES resources / enqueues (resource names ges_ress and ges_locks) can be obtained from V$RESOURCE_LIMIT. In case we are running out of reserved memory for GCS / GES related components, Oracle will dynamically allocate memory from the free memory pool in the shared pool. However, it is recommended to carefully calculate the resources and enqueues as needed since dynamic memory allocation from the shared pool is an expensive operation.
We recommend you monitor for more time to see if this limit is reach and it is a constant situation, then you could considered to increase the value of gcs_resources by instance.
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