oracle update太慢优化

tb_e_zw_nrllb_temp 量700225
gsm_user  量109398337

--优化前 两种update

--说明：gsm_user是视图存在GSM_USER_ID索引，tb_e_zw_nrllb_temp有user_id索引，使用以下两种方法都更新时间超5h+导致不能更新成功
--1
 update tb_e_zw_nrllb_temp t
   set t.msisdn = (select  msisdn from from gsm_user a
                  where to_char(a.GSM_USER_ID) = b.user_id
                  and b.settle_month = p_month_id))
   where .settle_month = p_month_id;
--2
merge into tb_e_zw_nrllb_temp t
  using gsm_user a
  on (to_char(a.GSM_USER_ID) = t.user_id  )
  when matched then
     update set
       t.msisdn =   a.MSISDN
     where t.settle_month = p_month_id;
 commit;

--优化后  

--优化后时间耗费主要在insert上，insert的select查询比较快，因此又想办法优化insert，大致如下

--修改insert表为nologging，使用 hint append，使用parallel，原本insert执行时间为25分钟，优化后执行时间为12分钟
 execute immediate  'truncate table TB_E_ZW_NRLLB_TEMP_msisdn';
     
      insert /*+ append*/ into TB_E_ZW_NRLLB_TEMP_msisdn
      select  a.GSM_USER_ID,a.MSISDN from gsm_user a
        where  exists (select 1 from tb_e_zw_nrllb_temp b
                  where to_char(a.GSM_USER_ID) = b.user_id
                  and b.settle_month = p_month_id) ;
       
       commit;
       sp_write_infolog('sp_sp_rep_sptc', '0', 'MSISDN临时表插入完成');
  --update耗时不超一分钟  
 merge into tb_e_zw_nrllb_temp t
  using (select distinct a.user_id,a.msisdn from TB_E_ZW_NRLLB_TEMP_msisdn a ) b
  on (b.user_id = t.user_id  )
  when matched then
     update set
       t.msisdn =   b.MSISDN
     where t.settle_month = p_month_id;
           
  commit;