[오라클] "PARALLEL" optimizer hint

OLTP 환경에서는 거의 사용될 일이 없지만 DW나 야간배치 작업성 없무에서는
parallel 힌트를 이용한 병렬 처리가 성능 향상에 도움이 많이 되더군요.
전 parallel 이란 스펠링이 잘 생각이 나지 않죠. 가끔 사용할려고 하면 떠오르지 않아
난감할때가 더러 있더라구요. ^^

형식) SELECT /*+ PARALLEL(A 3) */ FROM MEMBER A

The PARALLEL hint must use the table alias if an alias is specified in the query. The hint can then take two values separated by commas after the table name. The first value specifies the degree of parallelism for the given table, the second value specifies how the table is to be split among the instances of a parallel server. Specifying DEFAULT or no value signifies that the query coordinator should examine the settings of the initialization parameters (described in a later section) to determine the default degree of parallelism.

In the following example, the PARALLEL hint overrides the degree of parallelism specified in the emp table definition:

SELECT /*+ FULL(scott_emp) PARALLEL(scott_emp, 5) */ ename
FROM scott.emp scott_emp;

In the next example, the PARALLEL hint overrides the degree of parallelism specified in the emp table definition and tells the optimizer to use the default degree of parallelism determined by the initialization parameters. This hint also specifies that the table should be split among all of the available instances, with the default degree of parallelism on each instance.

SELECT /*+ FULL(scott_emp) PARALLEL(scott_emp, DEFAULT,DEFAULT) */ ename
FROM scott.emp scott_emp;