3

我们有两个巨大的表并试图更新大约 6000 万条记录。以前是 30 分钟更新一次，现在需要几个小时 n 个小时，甚至不超过 20% 的数据增长。这里有更多信息。我看到“单元单块物理读取”“PX Deq：Table Q Normal”事件有很多等待。我不明白为什么并行提示不起作用。这是单元单块物理读取的原因吗？还是有任何其他原因导致性能下降，有什么想法吗？是否有理由通过摆脱“WHERE EXISTS”子句来提高性能？

table1(A) 大小 316 GB 记录数 456,365,654

表 2(B) 7GB 记录数 31,934,956

   UPDATE /*+  parallel (a, 8) */
          table1 a
       SET (c_age,
            c_age_de,
            wa_only_ind) =
              (SELECT c_age,
                      c_age_de,
                      wa_only_ind
                 FROM table2 b
                WHERE     B.ip = A.ip
                      AND a.c_age IS NULL
                      AND b.o_type IN ('TYPE12', 'TYPE14'))
     WHERE EXISTS
              (SELECT 1
                 FROM table2 b2
                WHERE     b2.ip = a.ip
                      AND a.c_age IS NULL
                      AND b2.o_type IN ('TYPE12', 'TYPE14'));

解释计划

   ----------------------------------------------------------------------------------------------------------------------------------------------------------
    | Id  | Operation                        | Name                    | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | Pstart| Pstop |    TQ  |IN-OUT| PQ Distrib |
    ----------------------------------------------------------------------------------------------------------------------------------------------------------
    |   0 | UPDATE STATEMENT                 |                         |     17M|  9599M|  5076M (20)|999:59:59 |       |       |        |      |            |
    |   1 |  UPDATE                          | TABLE1                  |        |       |            |          |       |       |        |      |            |
    |   2 |   PX COORDINATOR                 |                         |        |       |            |          |       |       |        |      |            |
    |   3 |    PX SEND QC (RANDOM)           | :TQ10002                |     17M|  9599M|  1069K  (1)| 04:09:40 |       |       |  Q1,02 | P->S | QC (RAND)  |
    |*  4 |     HASH JOIN RIGHT SEMI BUFFERED|                         |     17M|  9599M|  1069K  (1)| 04:09:40 |       |       |  Q1,02 | PCWP |            |
    |   5 |      PX RECEIVE                  |                         |     29M|   476M| 23984   (2)| 00:05:36 |       |       |  Q1,02 | PCWP |            |
    |   6 |       PX SEND HASH               | :TQ10000                |     29M|   476M| 23984   (2)| 00:05:36 |       |       |  Q1,00 | P->P | HASH       |
    |   7 |        PX BLOCK ITERATOR         |                         |     29M|   476M| 23984   (2)| 00:05:36 |       |       |  Q1,00 | PCWC |            |
    |*  8 |         TABLE ACCESS STORAGE FULL| TABLE2                  |     29M|   476M| 23984   (2)| 00:05:36 |       |       |  Q1,00 | PCWP |            |
    |   9 |      PX RECEIVE                  |                         |     57M|    30G|  1045K  (1)| 04:04:04 |       |       |  Q1,02 | PCWP |            |
    |  10 |       PX SEND HASH               | :TQ10001                |     57M|    30G|  1045K  (1)| 04:04:04 |       |       |  Q1,01 | P->P | HASH       |
    |  11 |        PX BLOCK ITERATOR         |                         |     57M|    30G|  1045K  (1)| 04:04:04 |     1 |     3 |  Q1,01 | PCWC |            |
    |* 12 |         TABLE ACCESS STORAGE FULL| TABLE1                  |     57M|    30G|  1045K  (1)| 04:04:04 |     1 |     6 |  Q1,01 | PCWP |            |
    |* 13 |   FILTER                         |                         |        |       |            |          |       |       |        |      |            |
    |* 14 |    TABLE ACCESS BY INDEX ROWID   | TABLE2                  |      1 |   210 |     4   (0)| 00:00:01 |       |       |        |      |            |
    |* 15 |     INDEX RANGE SCAN             | TABLE2_IDX1             |      1 |       |     3   (0)| 00:00:01 |       |       |        |      |            |
    ----------------------------------------------------------------------------------------------------------------------------------------------------------


Predicate Information (identified by operation id):
---------------------------------------------------

   4 - access("B2"."IP"="A"."IP")
   8 - storage("B2"."O_TYPE"='TYPE1' OR "B2"."O_TYPE"='TYPE12')
       filter("B2"."O_TYPE"='TYPE1' OR "B2"."O_TYPE"='TYPE12')
  12 - storage("A"."C_AGE" IS NULL)
       filter("A"."C_AGE" IS NULL)
  13 - filter(:B1 IS NULL)
  14 - filter("B"."O_TYPE"='TYPE1' OR "B"."O_TYPE"='TYPE12')
  15 - access("B"."IP"=:B1)


 SQL_ID  dd0ah20057j37
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                        | Name                         | E-Rows |E-Bytes| Cost (%CPU)| E-Time   | Pstart| Pstop |    TQ  |IN-OUT| PQ Distrib |  OMem |  1Mem |  O/1/M   |
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | UPDATE STATEMENT                 |                              |        |       |    43T(100)|          |       |       |        |      |            |       |       |          |
|   1 |  UPDATE                          | TABLE1                   |        |       |            |          |       |       |        |      |            |       |       |          |
|   2 |   PX COORDINATOR                 |                              |        |       |            |          |       |       |        |      |            |       |       |          |
|   3 |    PX SEND QC (RANDOM)           | :TQ10002                     |     57M|    31G| 65326   (3)| 00:14:16 |       |       |  Q1,02 | P->S | QC (RAND)  |       |       |          |
|*  4 |     HASH JOIN RIGHT SEMI BUFFERED|                              |     57M|    31G| 65326   (3)| 00:14:16 |       |       |  Q1,02 | PCWP |            |  1537M|    25M|     2/0/0|
|   5 |      PX RECEIVE                  |                              |     32M|   550M|  2190  (20)| 00:00:29 |       |       |  Q1,02 | PCWP |            |       |       |          |
|   6 |       PX SEND HASH               | :TQ10000                     |     32M|   550M|  2190  (20)| 00:00:29 |       |       |  Q1,00 | P->P | HASH       |       |       |          |
|   7 |        PX BLOCK ITERATOR         |                              |     32M|   550M|  2190  (20)| 00:00:29 |       |       |  Q1,00 | PCWC |            |       |       |          |
|*  8 |         TABLE ACCESS STORAGE FULL| TABLE2 P1      |     32M|   550M|  2190  (20)| 00:00:29 |       |       |  Q1,00 | PCWP |            |  1025K|  1025K|     2/0/0|
|   9 |      PX RECEIVE                  |                              |     57M|    30G| 63100   (2)| 00:13:47 |       |       |  Q1,02 | PCWP |            |       |       |          |
|  10 |       PX SEND HASH               | :TQ10001                     |     57M|    30G| 63100   (2)| 00:13:47 |       |       |  Q1,01 | P->P | HASH       |       |       |          |
|  11 |        PX BLOCK ITERATOR         |                              |     57M|    30G| 63100   (2)| 00:13:47 |     1 |     3 |  Q1,01 | PCWC |            |       |       |          |
|* 12 |         TABLE ACCESS STORAGE FULL| TABLE1                   |     57M|    30G| 63100   (2)| 00:13:47 |     1 |     6 |  Q1,01 | PCWP |            |  1025K|  1025K|     2/0/0|
|* 13 |   FILTER                         |                              |        |       |            |          |       |       |        |      |            |       |       |          |
|* 14 |    TABLE ACCESS BY INDEX ROWID   | TABLE2          |    320K|   113M| 12787   (1)| 00:02:48 |       |       |        |      |            |       |       |          |
|* 15 |     INDEX RANGE SCAN             | TABLE2_IDX1          |    128K|       |     4  (25)| 00:00:01 |       |       |        |      |            |  1025K|  1025K|          |
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   4 - access("U2"."IP"="I"."IP")
   8 - storage(:Z>=:Z AND :Z<=:Z AND (("U2"."OPERATION_TYPE"='TYPE1' OR "U2"."OPERATION_TYPE"='TYPE12')))
       filter(("U2"."OPERATION_TYPE"='TYPE1' OR "U2"."OPERATION_TYPE"='TYPE12'))
  12 - storage(:Z>=:Z AND :Z<=:Z AND "I"."AGE" IS NULL)
       filter("I"."AGE" IS NULL)
  13 - filter(:B1 IS NULL)
  14 - filter(("U"."OPERATION_TYPE"='TYPE1' OR "U"."OPERATION_TYPE"='TYPE12'))
  15 - access("U"."IP"=:B1)

Plan hash value: 1669240984

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                         | Name                    | E-Rows |E-Bytes|E-Temp | Cost (%CPU)| E-Time   | Pstart| Pstop |    TQ  |IN-OUT| PQ Distrib |  OMem |  1Mem |  O/1/M   |
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
|   0 | MERGE STATEMENT                   |                         |        |       |       |   374K(100)|          |       |       |        |      |            |       |       |          |
|   1 |  MERGE                            | TABLE1                    |        |       |       |            |          |       |       |        |      |            |       |       |          |
|   2 |   PX COORDINATOR                  |                         |        |       |       |            |          |       |       |        |      |            |       |       |          |
|   3 |    PX SEND QC (RANDOM)            | :TQ10002                |    413M|   574G|       |   374K  (2)| 01:21:50 |       |       |  Q1,02 | P->S | QC (RAND)  |       |       |          |
|   4 |     VIEW                          |                         |        |       |       |            |          |       |       |  Q1,02 | PCWP |            |       |       |          |
|*  5 |      HASH JOIN BUFFERED           |                         |    413M|   574G|  3583M|   374K  (2)| 01:21:50 |       |       |  Q1,02 | PCWP |            |  2047M|   100M|          |
|   6 |       PX RECEIVE                  |                         |     32M|    27G|       |  2199  (20)| 00:00:29 |       |       |  Q1,02 | PCWP |            |       |       |          |
|   7 |        PX SEND HASH               | :TQ10000                |     32M|    27G|       |  2199  (20)| 00:00:29 |       |       |  Q1,00 | P->P | HASH       |       |       |          |
|   8 |         PX BLOCK ITERATOR         |                         |     32M|    27G|       |  2199  (20)| 00:00:29 |       |       |  Q1,00 | PCWC |            |       |       |          |
|*  9 |          TABLE ACCESS STORAGE FULL| TABLE2           |     32M|    27G|       |  2199  (20)| 00:00:29 |       |       |  Q1,00 | PCWP |            |  1025K|  1025K|     2/0/0|
|  10 |       PX RECEIVE                  |                         |    413M|   218G|       | 67413   (9)| 00:14:44 |       |       |  Q1,02 | PCWP |            |       |       |          |
|  11 |        PX SEND HASH               | :TQ10001                |    413M|   218G|       | 67413   (9)| 00:14:44 |       |       |  Q1,01 | P->P | HASH       |       |       |          |
|  12 |         PX BLOCK ITERATOR         |                         |    413M|   218G|       | 67413   (9)| 00:14:44 |     1 |     3 |  Q1,01 | PCWC |            |       |       |          |
|* 13 |          TABLE ACCESS STORAGE FULL| TABLE1              |    413M|   218G|       | 67413   (9)| 00:14:44 |     1 |     6 |  Q1,01 | PCWP |            |  1025K|  1025K|     2/0/0|
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   5 - access("I"."IP"="U"."IP")
   9 - storage(:Z>=:Z AND :Z<=:Z AND (("U"."OPERATION_TYPE"='TYPE1' OR "U"."OPERATION_TYPE"='TYPE12')))
       filter(("U"."OPERATION_TYPE"='TYPE1' OR "U"."OPERATION_TYPE"='TYPE12'))
  13 - storage(:Z>=:Z AND :Z<=:Z)
4

1 回答 1

3
  1. alter session enable parallel dml;当前计划中只有一部分是并行运行的。UPDATE操作应该在操作之下，PX COORDINATOR而不是之上。这可能是因为会话没有启用并行 DML。

下面是一个示例模式和查询，展示了启用会话并行性时计划如何变化。

drop table test1 purge;
create table test1(a number not null, b number);
insert into test1 select level, 1 from dual connect by level <= 100000;
begin
    dbms_stats.gather_table_stats(user, 'TEST1');
end;
/

alter session disable parallel dml;
explain plan for update /*+ parallel(test1, 8) */ test1 set a = 1 where b <= 1000;
select * from table(dbms_xplan.display);

---------------------------------------------------------------------------------------------------------------
| Id  | Operation             | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------
|   0 | UPDATE STATEMENT      |          |   100K|   781K|    11  (10)| 00:00:01 |        |      |            |
|   1 |  UPDATE               | TEST1    |       |       |            |          |        |      |            |
|   2 |   PX COORDINATOR      |          |       |       |            |          |        |      |            |
...

rollback;
alter session enable parallel dml;
explain plan for update /*+ parallel(test1, 8) */ test1 set a = 1 where b <= 1000;
select * from table(dbms_xplan.display);


---------------------------------------------------------------------------------------------------------------
| Id  | Operation             | Name     | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
---------------------------------------------------------------------------------------------------------------
|   0 | UPDATE STATEMENT      |          |   100K|   781K|    11  (10)| 00:00:01 |        |      |            |
|   1 |  PX COORDINATOR       |          |       |       |            |          |        |      |            |
|   2 |   PX SEND QC (RANDOM) | :TQ10000 |   100K|   781K|    11  (10)| 00:00:01 |  Q1,00 | P->S | QC (RAND)  |
|   3 |    UPDATE             | TEST1    |       |       |            |          |  Q1,00 | PCWP |            |
...
  1. MERGE 您的评论说您已经尝试过 a MERGE，但结合其他提示可能值得再次尝试。 MERGE允许 TABLE2 只列出一次，删除一个连接。并且MERGE支持比 更多的连接方法UPDATE，例如修改后的表和其他行源之间的哈希连接。
  2. 语句级并行提示。从 11gR2 开始，对象几乎不应该列在并行提示中。如果未列出对象，则提示适用于整个语句。如果在语句的一部分中使用并行性，那么在任何地方都使用它几乎没有什么坏处。替换/*+ parallel (a, 8) */为/*+ parallel (8) */。
  3. 发生了什么变化？ 即使上述提示有所帮助，了解发生了什么变化并导致了性能问题仍然是件好事。如果计划发生变化，则应在 AWR 中捕获不同的计划。用以下语句找到它们： select * from table(dbms_xplan.display_awr(sql_id => 'Your SQL_ID')); 仅计划是不够的，尤其是在数据仓库中。可能需要通过在操作级别聚合等待事件来比较运行。所有信息都在其中，DBA_HIST_ACTIVE_SESS_HISTORY但需要自定义查询。
于 2014-09-11T02:13:50.173 回答