Role of Parallel Execution


Role of Parallel Execution

With its parallel execution features, Oracle can divide the work of processing certain types of SQL statements among multiple query server processes. 

OPS provide the framework for parallel execution to work between nodes. Parallel execution features behave the same way in Oracle with or without the Parallel Server Option. The only difference is that OPS enables multiple nodes to execute on behalf of a single query or other parallel operation. 

In some applications, notably data warehousing applications, individual queries consume a great deal of CPU resources and require significant disk 1/0, unlike most online insert or update transactions. To take advantage of multiprocessing systems, the data server must parallelize individual queries into units of work that .can be processed simultaneously. 

example of Parallel Execution  processing

If the query was not processed in pa r alle-, disks would be read serially with a single I/O. A single CPU would have to scan all rows in the LINE_ITEMS table and total the revenues across all rows. With the query parallelized, disks are read in parallel, With multiple I/Os. Several CPUs can scan a part of the table in parallel and aggregate the results. Parallel query benefits not only from multiple CPUs but also from more of t e available I/O bandwidth.