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 trace16:14:20 SCOTT@ test1 >select sum(sal) from 本文来源gaodai#ma#com搞*!代#%^码$网*emp2 group by deptnoElapsed: 00:00:00.01Execution 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
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