Which three tasks are performed by the parallel execution coordinator process?
A.
Allocating parallel execution processes from the parallel execution server pool.
B.
Determining the parallel execution method for each operation in the execution plan.
C.
Managing the data flow between the producers and consumers during inter-operation
parallelism.
D.
Any serial processing that is part of the execution plan.
E.
Determining the desired number of parallel execution processes
F.
Managing the data flow between the producers and consumers during intra-operation
parallelism.
Explanation:
A: When executing a parallel operation, the parallel execution coordinator obtains
parallel execution servers from the pool and assigns them to the operation. If necessary, Oracle
Database can create additional parallel execution servers for the operation. These parallel
execution servers remain with the operation throughout execution. After the statement has been
processed completely, the parallel execution servers return to the pool.
B:
* The parallel execution coordinator examines each operation in a SQL statement’s execution plan
then determines the way in which the rows operated on by the operation must be divided or
redistributed among the parallel execution servers.
* After the optimizer determines the execution plan of a statement, the parallel executioncoordinator determines the parallel execution method for each operation in the plan.
Note:
* Oracle Database can process a parallel operation with fewer than the requested number of
processes. If all parallel execution servers in the pool are occupied and the maximum number of
parallel execution servers has been started, the parallel execution coordinator switches to serial
processing.
Reference: Oracle Database VLDB and Partitioning Guide 11g, How Parallel Execution Works
why not D ?
When the parallel servers are finished executing the statement, the query coordinator performs any portion of the work that cannot be executed in parallel. For example, a parallel query with a SUM() operation requires adding the individual subtotals calculated by each parallel server.
A,B,D correct imo
A,B, and D.
On D, note point 4 below:
https://docs.oracle.com/cd/E11882_01/server.112/e25523/parallel002.htm#i1006328
A B E
After the optimizer determines the execution plan of a statement, the parallel execution coordinator determines the parallel execution method for each operation in the plan. For example, the parallel execution method might be to perform a parallel full table scan by block range or a parallel index range scan by partition. The coordinator must decide whether an operation can be performed in parallel and, if so, how many parallel execution servers to enlist. The number of parallel execution servers in one set is the degree of parallelism (DOP).
A,D,E ?
A+B+E IMHO
https://docs.oracle.com/cd/B19306_01/server.102/b14223/usingpe.htm
The query coordinator does the following:
— Parses the query and determines the degree of parallelism
A — Allocates one or two set of slaves (threads or processes)
— Controls the query and sends instructions to the PQ slaves
— Determines which tables or indexes need to be scanned by the PQ slaves
— Produces the final output to the user
D is for:
Oracle Database can process a parallel operation with fewer than the requested number of processes. If all parallel execution servers in the pool are occupied and the maximum number of parallel execution servers has been started, the parallel execution coordinator switches to serial processing.