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无语的index hint:手工分配哈希区,5小时不出结果,优化后20分钟

同事发来一个语句,说5个小时不出结果,我滴个神呀,想看看到底是什么垃圾语句造成的。于是叫同事发过来。不看不知道,一看吓一跳,3个表关联,强制使用了2个index hint,其中一个表9g,一个表67g,还有一个小表40Mb。无知的开发人员,以为走index就是快的,哎。。。
下面是同事发来的语句: 
select /*+  parallel(t,4) index(a,IDX_COMMBASUBSHIST_1) index(b,IDX_COMMCMSERVHIST_1)*/
    1,
    t.DISC_ID,
    t.DISC_LEV,
    to_date(20140117082042, 'yyyymmddhh24miss'),
    t.MSINFO_ID,
    t.ORG_ID,
    t.SERV_ID,
    t.SUBS_ID,
    t.OBJ_GRP_ID,
    a.SUBS_CODE,
    a.SUBS_STAT,
    a.SUBS_STAT_REASON,
    a.SUBS_STAT_DATE,
    a.ACTION_ID,
    a.ACTION_TYPE,
    a.ACTION_EX_TYPE,
    a.ACT_DATE,
    a.REQ_ID,
    a.STAFF_ID,
    a.CMMS_CUST_CODE,
    a.SPEED_VALUE,
    b.ACC_NBR,
    b.CUST_ID,
    b.SERV_NBR,
    b.CONSUME_GRADE,
    b.SERV_LEV,
    b.ACCOUNT_NBR,
    b.CITY_VILLAGE_ID,
    b.SERV_CHANNEL_ID,
    b.SERV_STAT_ID,
    b.CUST_CLASS_DL,
    b.CUST_TYPE_ID,
    b.USER_TYPE,
    b.USER_CHAR,
    b.PAYMENT_TYPE,
    b.BILLING_TYPE,
    b.PROD_ID,
    b.PROD_CAT_ID,
    b.EXCHANGE_ID,
    b.SERV_COL1,
    b.SERV_COL2,
    b.AREA_ID,
    b.SUBST_ID,
    b.BRANCH_ID,
    b.STOP_TYPE,
    b.CUST_MANAGER_ID,
    b.CREATE_DATE,
    b.ADDRESS_ID,
    b.SUBS_DATE,
    b.OPEN_DATE,
    b.MODI_STAFF_ID,
    b.CMMS_CUST_ID,
    b.CUST_NAME,
    b.SALES_ID,
    b.SALES_TYPE_ID,
    b.SERV_ADDR_ID,
    t.HIST_CREATE_DATE,
    b.ARREAR_MONTH,
    b.ARREAR_MONTH_LAST,
    t.SALESTAFF_ID,
    t.EHOME_TYPE,
    t.EHOME_CLASS,
    b.strat_grp_dl,
    b.sale_org1,
    b.sale_org2,
    b.sale_org3,
    b.location_type,
    b.region_flag,
    b.terminal_id,
    b.pstn_id,
    b.fee_id,
    b.payment_id,
    b.billing_id,
    b.strat_grp_xl,
    b.fld1,
    b.fld3,
    b.cust_level,
    b.group_cust_type,
    b.cust_region,
    b.group_cust_grade,
    b.control_level,
    b.net_connect_type,
    b.trade_type_id,
    b.acc_nbr2,
    b.cdma_class_id,
    b.phone_number_id,
    b.develop_channel,
    b.online_time,
    t.wireless_type,
    b.new_serv_stat_id,
    b.is_phs_tk,
    b.serv_grp_type,
    b.state,
    t.cdma_disc_type,
    b.mix_disc,
    b.is_3g,
    t.add_disc_type,
    to_number(nvl(b.business_type, '-1')),
    nvl(t.label_num, -1),
    b.is_mix_prod,
    t.price_id,
    t.disc_item_id,
    b.STD_SUBST_ID,
    b.STD_BRANCH_ID,
    t.DISC_ITEM_ID_OP,
    t.PRICE_ID_OP,
    t.business_type,
    b.new_prod_id,
    b.BOARD_SUBST_ID,
    b.BOARD_BRANCH_ID
     from RPT_COMM_BA_SUBS_HIST  a,
          RPT_COMM_CM_SERV_HIST  b,
          TB_COMM_BA_MSDISC_TEMP t
    where a.subs_id = t.subs_id
      and b.serv_id = t.serv_id



--同事说开销比较大。有450W。。下面是执行计划:
<img src=http://www.mamicode.com/"http://img.blog.csdn.net/20141025102001913?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvZ2RtemxoajE=/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />>
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无语的index hint:手工分配哈希区,5小时不出结果,优化后20分钟