When you create indexes and tables in parallel, each parallel execution server allocates a new extent and fills the extent with the table or index data.įor example, if you create an index with a DOP of 4, then the index has at least four extents initially. In all cases where the query cannot execute in parallel because of any of these restrictions, the whole query executes serially without giving an error message. Parallel DML and parallel DDL are not supported with object types, and such statements are always performed serially. Without a MAP function, the query is automatically executed serially. The following restrictions apply to using parallel query for object types:Ī MAP function is needed to execute queries in parallel for queries involving joins and sorts (through ORDER BY, GROUP BY, or set operations). There are no limitations on the size of the object types for parallel queries. PL/SQL and Oracle Call Interface (OCI) queries for object types
Parallel query for object types supports all of the features that are available for sequential queries on object types, including:Ĭonstructors to create object type instances Parallel queries can be performed on object type tables and tables containing object type columns. Parallel Queries on Index-Organized Tables This section contains the following topics:
If the parallel DDL statement includes a subquery, the subquery's DOP is equivalent to the DDL operation. If the parallel DML statement includes a subquery, the subquery's DOP is equivalent to that for the DML operation.įor parallel DDL, the reference object that determines the DOP is the table, index, or partition being created, rebuilt, split, or moved. Parallel DML also adds some limits to the DOP to prevent deadlock. The basic rule is to pick the table or index with the largest DOP.įor parallel DML ( INSERT, UPDATE, MERGE, and DELETE), the reference object that determines the DOP is the table being modified by an insert, update, or delete operation. Parallel query looks at each table and index, in the portion of the query to be executed in parallel, to determine which is the reference table. To determine the DOP, Oracle Database looks at the reference objects: These components are determined differently for queries, DDL operations, and DML operations. The parallelization decision for SQL queries has two components: the decision to parallelize and the degree of parallelism (DOP). You can also query external tables in parallel. You can use parallel queries and parallel subqueries in SELECT statements and execute in parallel the query portions of DDL statements and DML statements ( INSERT, UPDATE, and DELETE).
0 kommentar(er)
