oracle insert 并行插入优化

Parallel DML Tip 1: INSERT

The functionality available using an INSERT statement can be summarized as shown in Table 8-5:

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Table 8-5 Summary of INSERT Features

Insert Type	Parallel	Serial	NOLOGGING
Conventional	No See text in this section for information about using the NOAPPEND hint with parallel DML enabled to perform a parallel conventional insert.	Yes	No
Direct-path INSERT (APPEND)	Yes, but requires ALTER SESSION ENABLE PARALLEL DML or the ENABLE_PARALLEL_DML SQL hint to enable PARALLEL DML mode and one of the following: Table PARALLEL attribute or PARALLEL hint to explicitly set parallelism APPEND hint to explicitly set mode Or the following ALTER SESSION FORCE PARALLEL DML to force PARALLEL DML mode	Yes, but requires: APPEND hint	Yes, but requires: NOLOGGING attribute set for partition or table

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If parallel DML is enabled and there is a PARALLEL hint or PARALLEL attribute set for the table in the data dictionary, then insert operations are parallel and appended, unless a restriction applies. If either the PARALLEL hint or PARALLEL attribute is missing, the insert operation is performed serially. Automatic DOP only parallelizes the DML part of a SQL statement if and only if parallel DML is enabled or forced.

If parallel DML is enabled, then you can use the NOAPPEND hint to perform a parallel conventional insert operation. For example, you can use /*+ noappend parallel */ with the SQL INSERT statement to perform a parallel conventional insert.

SQL> INSERT /*+ NOAPPEND PARALLEL */ INTO sales_hist SELECT * FROM sales;

The advantage of the parallel conventional insert operation is the ability to perform online operations with none of the restrictions of direct-path INSERT. The disadvantage of the parallel conventional insert operation is that this process may be slower than direct-path INSERT.