parallel_clause lets you parallelize the creation of a database object and set the default degree of parallelism for subsequent queries of and DML operations on the object.
You can specify the
parallel_clause in the following statements:
TABLE: to set parallelism for the table (see CREATE TABLE).
TABLE (see ALTER TABLE):
To change parallelism for the table
To parallelize the operations of adding, coalescing, exchanging, merging, splitting, truncating, dropping, or moving a table partition
INDEX: to set parallelism for the index (see CREATE INDEX).
INDEX (see ALTER INDEX):
To change parallelism for the index
To parallelize the rebuilding of the index or the splitting of an index partition
VIEW: to set parallelism for the materialized view (see CREATE MATERIALIZED VIEW).
VIEW (see ALTER MATERIALIZED VIEW):
To change parallelism for the materialized view
To parallelize the operations of adding, coalescing, exchanging, merging, splitting, truncating, dropping, or moving a materialized view partition
To parallelize the operations of adding or moving materialized view subpartitions
LOG: to set parallelism for the materialized view log (see CREATE MATERIALIZED VIEW LOG).
LOG (see ALTER MATERIALIZED VIEW LOG):
To change parallelism for the materialized view log
To parallelize the operations of adding, coalescing, exchanging, merging, splitting, truncating, dropping, or moving a materialized view log partition
RECOVER: to recover the database (see ALTER DATABASE).
standby_database_clauses: to parallelize operations on the standby database (see ALTER DATABASE).
This section describes the semantics of the
parallel_clause. For additional information, refer to the SQL statement in which you set or reset parallelism for a particular database object or operation.
Note:The syntax of the
parallel_clausesupersedes syntax appearing in earlier releases of Oracle. Superseded syntax is still supported for backward compatibility but may result in slightly different behavior from that documented.
PARALLEL if you want Oracle to select a degree of parallelism equal to the number of CPUs available on all participating instances times the value of the
PARALLEL_THREADS_PER_CPU initialization parameter.
PARALLEL integer Specification of
integer indicates the degree of parallelism, which is the number of parallel threads used in the parallel operation. Each parallel thread may use one or two parallel execution servers. Normally Oracle calculates the optimum degree of parallelism, so it is not necessary for you to specify
Parallelism is disabled for DML operations on tables on which you have defined a trigger or referential integrity constraint.
When you specify the
parallel_clause during creation of a table, if the table contains any columns of LOB or user-defined object type, then subsequent
MERGE operations that modify the LOB or object type column are executed serially without notification. Subsequent queries, however, will be executed in parallel.
A parallel hint overrides the effect of the
DML statements and
SELECT statements that reference remote objects can run in parallel. However, the remote object must really be on a remote database. The reference cannot loop back to an object on the local database, for example, by way of a synonym on the remote database pointing back to an object on the local database.
DML operations on tables with LOB columns can be parallelized. However, intrapartition parallelism is not supported.