Queries requiring large table scans, joins, or partitioned index scans
Creation of large indexes
Creation of large tables (including materialized views)
Bulk inserts, updates, merges, and deletes
You can also use parallel execution to access object types within an Oracle database. For example, you can use parallel execution to access large objects (LOBs).
The benefits of parallel execution can be seen in DSS and data warehousing environments. OLTP systems can also benefit from parallel execution during batch processing and during schema maintenance operations such as creation of indexes. The average simple DML or SELECT statements that characterize OLTP applications would not see any benefit from being executed in parallel.
Parallel execution is not normally useful for:
Environments in which the typical query or transaction is very short (a few seconds or less). This includes most online transaction systems. Parallel execution is not useful in these environments because there is a cost associated with coordinating the parallel execution servers; for short transactions, the cost of this coordination may outweigh the benefits of parallelism.
Environments in which the CPU, memory, or I/O resources are already heavily utilized. Parallel execution is designed to exploit additional available hardware resources; if no such resources are available, then parallel execution will not yield any benefits and indeed may be detrimental to performance.
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