Degree of Parallelism

After the decision to parallelize the SELECT or INSERT operation is made, one parallel directive is picked for deciding the DOP of the whole statement, using the following precedence rule Insert hint directive, then Session, then Parallel declaration specification of the inserting table, and then Maximum query directive.

In this context, maximum query directive means that among multiple tables and indexes, the table or index that has the maximum DOP determines the parallelism for the query operation.

In Example 8-6, the chosen parallel directive is applied to both the SELECT and INSERT operations. The DOP is specified as 2 in the PARALLEL hint for the INSERT statement and the DOP is specified as 4 in the PARALLEL hint for the SELECT statement.

Example 8-6 Parallelization: Example 3

INSERT /*+ PARALLEL(tbl_ins,2) */ INTO tbl_ins
SELECT /*+ PARALLEL(tbl_sel,4) */ * FROM tbl_sel;