PX SEND (PARTITION (KEY))

Description

Parallel execution - send rows to parent process based on partition key

Versions

This operation is implemented in the following versions

Example

This example was developed using Oracle 10.2.0.1 on Linux

This example requires the following table definitions

    CREATE TABLE t1
    (
      c1 NUMBER,
      c2 NUMBER,
      c3 NUMBER,
      c4 CHAR(100)
    )
    PARTITION BY RANGE (c1)
    (
      PARTITION p1 VALUES LESS THAN (10),
      PARTITION p2 VALUES LESS THAN (20),
      PARTITION p3 VALUES LESS THAN (30),
      PARTITION p4 VALUES LESS THAN (40)
    );

    CREATE TABLE t2
    (
      c1 NUMBER,
      c2 NUMBER,
      c3 NUMBER,
      c4 CHAR(100)
    )
    PARTITION BY RANGE (c1)
    (
      PARTITION p1 VALUES LESS THAN (10),
      PARTITION p2 VALUES LESS THAN (20),
      PARTITION p3 VALUES LESS THAN (30),
      PARTITION p4 VALUES LESS THAN (40)
    );

Dynamic sampling must be disabled using

    ALTER SESSION SET optimizer_dynamic_sampling = 0;

The statement

    SELECT /*+ PARALLEL (t1,4) */ t2.c2
    FROM t1,t2
    WHERE t1.c1 = t2.c1;

generates the following execution plan

0     SELECT STATEMENT Optimizer=CHOOSE
1   0   PX COORDINATOR
2   1     PX SEND (QC (RANDOM))
3   2       HASH JOIN
4   3         PX PARTITION RANGE (ALL)
5   4           TABLE ACCESS (FULL) OF 'T1'
6   3         BUFFER (SORT)
7   6           PX RECEIVE
8   7             PX SEND (PARTITION (KEY))
9   8               PARTITION RANGE (ALL)
10  9                 TABLE ACCESS (FULL) OF 'T2'