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 | 3 | 3 (34)| 00:00:01 | | | | | 1 | PX COORDINATOR | | | | | | | | | | 2 | PX SEND QC (RANDOM) | :TQ10001 | 14 | 3 | 3 (34)| 00:00:01 | Q1,01 | P->S | QC (RAND) | | 3 | HASH GROUP BY | | 14 | 3 | 3 (34)| 00:00:01 | Q1,01 | PCWP | | | 4 | PX RECEIVE | | 14 | 3 | 3 (34)| 00:00:01 | Q1,01 | PCWP | | | 5 | PX SEND HASH | :TQ10000 | 14 | 3 | 3 (34)| 00:00:01 | Q1,00 | P->P | HASH | | 6 | HASH GROUP BY | | 14 | 3 | 3 (34)| 00:00:01 | Q1,00 | PCWP | | | 7 | PX BLOCK ITERATOR | | 14 | 3 | 2 (0)| 00:00:01 | Q1,00 | PCWC | | | 8 | TABLE ACCESS FULL| EMP2 | 14 | 3 | 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

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