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Which two are benefits of In-Memory Parallel Execution?
A. Reduction in the duplication of block images across multiple buffer caches
B. Reduction in CPU utilization
C. Reduction in the number of blocks accessed
D. Reduction in physical I/O for parallel queries
E. Ability to exploit parallel execution servers on remote instance
Correct Answer: AC
Explanation/Reference:
Note:In-Memory Parallel Execution
When the parameter PARALLEL_DEGREE_POLICY is set to AUTO, Oracle Database decides if an object that is accessed using parallel execution would benefit from being cached in the SGA (also called the buffer cache). The decision to cache an object is based on a well-defined set of heuristics including the size of the object and frequency on which it is accessed. In an Oracle RAC environment, Oracle Database maps pieces of the object into each of the buffer caches on the active instances. By creating this mapping, Oracle Database automatically knows which buffer cache to access to find different parts or pieces of the object. Using this information, Oracle Database prevents multiple instances from reading the same information from disk over and over again, thus maximizing the amount of memory that can cache objects. If the size of the object is larger than the size of the buffer cache (single instance) or the size of the buffer cache multiplied by the number of active instances in an Oracle RAC cluster, then the object is read using directpath reads.
Reference:Oracle Database VLDB and Partitioning Guide11g,How Parallel Execution Works
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