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266 - Oracle Parallel Server

Oracle Parallel Server is a robust computing environment that harnesses the processing power of multiple, interconnected computers.
Oracle Parallel Server software and a collection of hardware known as a "cluster", unites the processing power of each component to become a single,
robust computing environment. A cluster generally comprises two or more computers, or "nodes".

In Oracle Parallel Server environments, all nodes concurrently execute transactions against the same database.
Oracle Parallel Server coordinates each node's access to the shared data to provide consistency and integrity.

PARALLEL_SERVERS_TARGET specifies the number of parallel server processes allowed to run parallel statements before statement queuing will be used.
When the parameter PARALLEL_DEGREE_POLICY is set to AUTO, Oracle will queue SQL statements that require parallel execution,
if the necessary parallel server processes are not available. Statement queuing will begin once the number of parallel server processes active
on the system is equal to or greater than PARALLEL_SERVER_TARGET.

SQL> alter system set PARALLEL_SERVERS_TARGET=5 scope=both;

PARALLEL_MAX_SERVERS specifies the maximum number of parallel execution processes and parallel recovery processes for an instance.
As demand increases, Oracle increases the number of processes from the number created at instance startup up to this value.

If you set this parameter too low, some queries may not have a parallel execution process available to them during query processing.
If you set it too high, memory resource shortages may occur during peak periods, which can degrade performance.

SQL> alter system set PARALLEL_MAX_SERVERS=16 scope=both;


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Story | by Dr. Radut