Quiz Post# 11: How many GES resources for a RAC instance?

How to measure the GES Resources (enqueues for RAC ) limit in RAC?

Oracle preserves the integrity of the users data during simultaneous use of the same data blocks by different instances using GCS. In addition to data blocks, many other shared resources can be concurrently accessed by end users. Oracle uses a queuing mechanism to ensure proper use of these shared resources. In an RAC environment , Global Enqueue services (GES) protects and regulate the access to these shared resources.

In typical single instance database, when you updating a controlfile (CF enqueue), of individual row (TX enqueue), or of an exclusive lock on a table (TM enqueue) will be created.   But in RAC environment as these resources (any of above) are shared these should be managed globally. GES protects and managing this enqueues with proper queueing mechanism. So typically enqueues are kind of locks, but here in RAC they were at SGA , i.e in memory structures.

We can keep dml_locks for an row based enqueue , but how about this GES enqueues.

Oracle will caculate the following while RAC instance startup for GES Resources:-

GES Resources= DB_FILES+DML_LOCKS+ENQUEUE_RESOURCES+PROCESSES+TRANSACTIONS+200) * 1 (1+(N-1) / N)

Where N is the number of instances.

You can see the GES_RESOURCES in v$resource_limit view for the maximum and current_utilization.