The most common use of parallel execution is in DSS and data warehousing
environments. Complex queries, such as those involving joins of several tables or
searches of very large tables, are often best executed in parallel.
Parallel execution is useful for many types of operations that access significant
amounts of data. Parallel execution improves processing for:
* Large table scans and joins
* Creation of large indexes
* Partitioned index scans
* Bulk inserts, updates, and deletes
* Aggregations and copying
You can also use parallel execution to access object types within an Oracle database.
For example, use parallel execution to access LOBs (large objects).
Parallel execution benefits systems that have all of the following characteristics:
* Symmetric multi-processors (SMP), clusters, or massively parallel systems
* Sufficient I/O bandwidth
* Underutilized or intermittently used CPUs (for example, systems where CPU usage is typically less than 30%)
* Sufficient memory to support additional memory-intensive processes such as sorts, hashing, and I/O buffers
If your system lacks any of these characteristics, parallel execution might not significantly improve performance. In fact, parallel execution can reduce system performance on overutilized systems or systems with small I/O bandwidth.
来自 “ ITPUB博客 ” ，链接：http://blog.itpub.net/26706/viewspace-64581/，如需转载，请注明出处，否则将追究法律责任。