Oracle使用并行踩过的坑
复制SQL>createtable emp2 asselect * from scott.emp; SQL>altertable emp2 parallel 2; --可以查看dba_tables表degree列 SQL>explainplan forselectsum(sal) from emp2 groupby deptno; SQL> select * fromtable(dbms_xplan.display()); PLAN_TABLE_OUTPUT -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Plan hash value: 3939201228 ------------------------------------------------------------------------------------------------------------------ | Id | Operation |Name | Rows | Bytes | Cost (%CPU)| Time | TQ |IN-OUT| PQ Distrib | ------------------------------------------------------------------------------------------------------------------ | 0| SELECT STATEMENT | | 1| 26 | 2 (0)| 00:00:01 | | | | | 1| PX COORDINATOR | | | | | | | | | | 2| PX SEND QC (RANDOM) | :TQ10001 | 1 | 26 | 2 (0)| 00:00:01 | Q1,使用01 | P->S |QC (RAND) | | 3| HASH GROUPBY | | 1 | 26 | 2 (0)| 00:00:01 | Q1,01 | PCWP | | | 4| PX RECEIVE | | 1 | 26 | 2 (0)| 00:00:01 | Q1,01 | PCWP | | | 5| PX SEND HASH | :TQ10000 | 1 | 26 | 2 (0)| 00:00:01 | Q1,00 | P->P |HASH | | 6| HASH GROUPBY | | 1 | 26 | 2 (0)| 00:00:01 | Q1,00 | PCWP | | | 7| PX BLOCK ITERATOR | | 1 | 26 | 2 (0)| 00:00:01 | Q1,00 | PCWC | | | 8| TABLE ACCESS FULL| EMP2 | 1 | 26 | 2 (0)| 00:00:01 | Q1,00 | PCWP | | ------------------------------------------------------------------------------------------------------------------ Note ----- -dynamic sampling used for this statement (level=2) 19 rows selected. 1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.20.21.22.23.24.25.26.27.28.29.30.31.