August 2000
Intermediate to advanced
288 pages
7h 50m
English
Content preview from Oracle Parallel Processing
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Overhead for Oracle Parallel Processing
As you might imagine, the benefits of parallel execution and Oracle Parallel Server do not come without a price. The next two sections discuss the various overhead issues that apply to parallel execution and Oracle Parallel Server.
Parallel Execution Overhead
Parallel execution entails a cost in terms of the processing overhead necessary to break up a task into pieces, manage the execution of each of those pieces, and combine the results when the execution is complete. Figure 1.8 illustrates some of the steps involved in parallel execution.
Figure 1-8. Steps in parallel execution
Parallel execution overhead can be divided into three areas: startup cost, interference, and skew.
Startup cost
Startup cost refers to the time it takes to start parallel execution of a query or a DML statement. It takes time and resources to divide one large task into smaller subtasks that can be run in parallel. Time also is required to create the processes needed to execute those subtasks and to assign each subtask to one of these processes. For a large query, this startup time may not be significant in terms of the overall time required to execute the query. For a small query, however, the startup time may end up being a significant portion of the total time.
Interference
Interference refers to the slowdown that one process imposes on other processes when accessing ...
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