STATUS CALIBRATION_TIME
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READY 13-APR-16 10.12.58.413 PM
再次执行看是否能使用自动并行度
SQL> set autotrace traceonly explain
SQL> select /*+ parallel */ * from emp;
Execution Plan
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Plan hash value: 2873591275
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| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib |
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| 0 | SELECT STATEMENT | | 14 | 532 | 2 (0)| 00:00:01 | | | |
| 1 | PX COORDINATOR | | | | | | | | |
| 2 | PX SEND QC (RANDOM)| :TQ10000 | 14 | 532 | 2 (0)| 00:00:01 | Q1,00 | P->S | QC (RAND) |
| 3 | PX BLOCK ITERATOR | | 14 | 532 | 2 (0)| 00:00:01 | Q1,00 | PCWC | |
| 4 | TABLE ACCESS FULL| EMP | 14 | 532 | 2 (0)| 00:00:01 | Q1,00 | PCWP | |
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Note
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- automatic DOP: Computed Degree of Parallelism is 2
可以看到在收集IO Calibration统计信息后，执行计划使用自动并行度。
当使用自动并行度，可以还需要调整一些调整参数。parallel_servers_target参数应该总是比parallel_max_servers参数值小，parallel_servers_target总是处于parallel_max_servers的75%到50%。如果开始看到大量并行度下降，那么应该使用这两个参灵敏的差距增大。