Distributed Transaction Restrictions

A DML operation cannot be parallelized if it is in a distributed transaction or if the DML or the query operation is against a remote object.

Examples of Distributed Transaction Parallelization

This section contains several examples of distributed transaction processing.

In this example, the DML statement queries a remote object:

INSERT /* APPEND PARALLEL (t3,2) */ INTO t3 SELECT * FROM t4@dblink;

The query operation is executed serially without notification because it references a remote object.

test之后，发现t4@dblink的query可以parallel，insert append无法parallel，就算不是Distributed Transaction 也不会parallel

In this example, the DML operation is applied to a remote object:

DELETE /*+ PARALLEL (t1, 2) */ FROM t1@dblink;

The DELETE operation is not parallelized because it references a remote object.

test：DELETE /*+ PARALLEL (t1, 2) */操作会在@dblink端parallel

Example 3 Distributed Transaction Parallelization

In this example, the DML operation is in a distributed transaction:

SELECT * FROM t1@dblink; 
DELETE /*+ PARALLEL (t2,2) */ FROM t2;
COMMIT; 

test：DELETE /*+ PARALLEL (t2,2) */操作会parallel

不知道官网上说的哪个版本，我的test是在10.2.0.4上做的

The DELETE operation is not parallelized because it occurs in a distributed transaction (which is started by the SELECT statement).

NOTE:Distributed Transaction 支持direct-path