Which two statements about In-Memory Parallel Execution are true?
A.
It can be configured using the Database Resource Manager.
B.
It increases the number of duplicate block images in the global buffer cache.
C.
It requires setting PARALLEL_DEGREE_POLICY to LIMITED.
D.
Objects selected for In-Memory Parallel Execution have blocks mapped to specific RAC
instances.
E.
It requires setting PARALLEL_DEGREE_POLICY to AUTO
F.
Objects selected for In-Memory Parallel Execution must be partitioned tables or indexes.
Explanation:
D, E: 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.
E: PARALLEL_DEGREE_POLICY specifies whether or not automatic degree of Parallelism,
statement queuing, and in-memory parallel execution will be enabled.
AUTO
Enables automatic degree of parallelism, statement queuing, and in-memory parallel execution.
Incorrect:
C:
LIMITED
Enables automatic degree of parallelism for some statements but statement queuing and inmemory Parallel Execution are disabled. Automatic degree of parallelism is only applied to those
statements that access tables or indexes decorated explicitly with the PARALLEL clause. Tables
and indexes that have a degree of parallelism specified will use that degree of parallelism.Reference: Oracle Database VLDB and Partitioning Guide 11g, How Parallel Execution Works
D+E.
http://docs.oracle.com/cd/E11882_01/server.112/e25523/parallel002.htm#CIHEFJGC
The initialization parameter PARALLEL_DEGREE_POLICY controls whether automatic degree of parallelism (DOP), parallel statement queuing, and in-memory parallel execution are enabled. This parameter has three possible values:
MANUAL – Disables automatic DOP, statement queuing and in-memory parallel execution. It reverts the behavior of parallel execution to what it was previous to Oracle Database 11g, Release 2 (11.2), which is the default.
LIMITED – Enables automatic DOP for some statements but parallel statement queuing and in-memory parallel execution are disabled. Automatic DOP is applied only to statements that access tables or indexes declared explicitly with the PARALLEL clause. Tables and indexes that have a DOP specified use that explicit DOP setting
AUTO – Enables automatic DOP, parallel statement queuing, and in-memory parallel execution.
and
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 direct-path reads.
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