Oracle Study之案例--Oracle Parallel Execution(并行执行)

OracleStudy之案例--OracleParallelExecution(并行执行)并行（Parallel）和OLAP系统并行的实现机制是：首先，Oracle会创建一个进程用于协调并行服务进程之间的信

。

案例分析：

查看并行服务执行计划

16:13:07 SCOTT@ test1 >create table emp2 as select * from emp; Table created. 16:13:26 SCOTT@ test1 >alter table emp2 parallel 2; Table altered. 16:13:37 SCOTT@ test1 >set autotrace trace 16:14:20 SCOTT@ test1 >select sum(sal) from emp2 group by deptno Elapsed: 00:00:00.01 Execution Plan ---------------------------------------------------------- Plan hash value: 3939201228 ------------------------------------------------------------------------------------------------------------------ | Id  | Operation                | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib | ------------------------------------------------------------------------------------------------------------------ |   0 | SELECT STATEMENT         |          |    14 |   364 |     3  (34)| 00:00:01 |        |      |            | |   1 |  PX COORDINATOR          |          |       |       |            |          |        |      |            | |   2 |   PX SEND QC (RANDOM)    | :TQ10001 |    14 |   364 |     3  (34)| 00:00:01 |  Q1,01 | P->S | QC (RAND)  | |   3 |    HASH GROUP BY         |          |    14 |   364 |     3  (34)| 00:00:01 |  Q1,01 | PCWP |            | |   4 |     PX RECEIVE           |          |    14 |   364 |     3  (34)| 00:00:01 |  Q1,01 | PCWP |            | |   5 |      PX SEND HASH        | :TQ10000 |    14 |   364 |     3  (34)| 00:00:01 |  Q1,00 | P->P | HASH       | |   6 |       HASH GROUP BY      |          |    14 |   364 |     3  (34)| 00:00:01 |  Q1,00 | PCWP |            | |   7 |        PX BLOCK ITERATOR |          |    14 |   364 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            | |   8 |         TABLE ACCESS FULL| EMP2     |    14 |   364 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            | ------------------------------------------------------------------------------------------------------------------ Note -----    - dynamic sampling used for this statement (level=2) Statistics ----------------------------------------------------------          12  recursive calls           0  db block gets           6  consistent gets           0  physical reads           0  redo size         471  bytes sent via SQL*Net to client         415  bytes received via SQL*Net from client           2  SQL*Net roundtrips to/from client           0  sorts (memory)           0  sorts (disk)           3  rows processed