???????Щ???????????????????????????????????????????????????RAC??????????????????????????????????н????????OS???????“???”??????????????????????????????????SQL?????д??/*+ parallel a??8*/  ????????RAC?????????????????256?????н????????????512?????н?????????????????????????????????????????????????????parallel_force_local=true????workaround???????????????????????????е??μ??
??????????????????????????????????????????￡????SQL??便???????????????н????
???????SQL?????????ж???3?????????????
????1)hint?????????ж?
????select /*+ parallel(a??8) */ * from scott.emp a order by ename;
????2)?????ж???????degree:
????select owner??table_name??degree from dba_tables where table_name='EMP';
????OWNER                          TABLE_NAME                     DEGREE
????------------------------------ ------------------------------ ----------
????3)auto DOP
?????????DOP = PARALLEL_THREADS_PER_CPU x CPU_COUNT
????RAC??DOP = PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT
????????????????hint>degree>auto DOP????????
????1?????hint???????ж?????????degree??
????2?????hint????parallel????д?????????????????DEGREE????DEFAULT????о??????(alter table scott.emp parallel?????????degree???)?????????auto DOP??
????????????????????Щ????
????1???????????group by???????????????????????ж?×2??
????2???????????ж?>parallel_max_servers????????ж?=0?????????У??????Pnnn????????
????3??RAC?У????ж?????????????????????????粢?ж?256??2??????????????????128?????н????
????“???ж?>parallel_max_servers”???ж?????????????С?
??????????Щ????????????????????
????1?????SQL????????hint????????degree=1???ж?=0;
????2?????SQL????????hint????????degree=DEFAULT ???ж?=PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT;
????3?????SQL????????hint????????degree>1 ???ж?=????degree;
????4?????SQL?????????????hint(/*+ parallel */ )?????????degree????????????ж?= PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT;
????5?????SQL???????????hint(/*+ parallel (a??8)*/ or /*+ parallel (a 8)*/ )?????????degree????????????ж?= hint?е????(8);
????6??????????????????????ж?×2;
????7?????ж????????RAC??????????ж?>parallel_max_servers?????ж?=0;
???????????????????hint??д??д?????д????/*+ parallel a??8*/?????????/*+ parallel a*/??????????????????8??
??????????????????ж?= PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT;
???????????????group by??????????ж?= PARALLEL_THREADS_PER_CPU x CPU_COUNT x INSTANCE_COUNT × 2??