月归档：五月 2018

使用_unnest_subquery优化sql

发表于 2018 年 5 月 17 日 由 惜分飞

一个复杂的sql查询,使用了大量EXISTS和NOT EXISTS 关联导致sql执行效率低下,这里挑选出来最核心的部分进行演示

SQL> explain plan for   select  
  2   a.aab034, a.aac001
  3    from si_dp.ac01_ac02 a
  4   where exists (select 1
  5            from ic40
  6           where aac001 = a.aac001
  7             and aae045 <= '201803'
  8             and aae120 = '0')
  9     and not exists (select 1
 10            from ic15
 11           where aac001 = a.aac001
 12             and aae002 <= '201803')
 13     and not EXISTS (select aab001
 14            from ab01
 15           where aab019 in ('91', '93')
 16             AND aab001 = a.aab001)
 17    and exists (select 1
 18            from ac13
 19           where aac001 = a.aac001
 20             and aae140 = '11'
 21             and aae114 in ('0', '1')
 22             and aae002 <= '201803')
 23     AND EXISTS (SELECT 1
 24            FROM AC13
 25           WHERE AAC001 = A.AAC001
 26             and aae140 = '11'
 27             AND AAE143 = '02'
 28             AND AAE003 < '201707'
 29             AND AAE002 BETWEEN '201801' AND '201803'
 30             and aae114 = '1')
 31     AND not EXISTS (SELECT 1
 32         FROM AC13
 33           WHERE AAC001 = A.AAC001
 34             and aae140 = '11'
 35          AND AAE002 < '201801')
 36     AND not EXISTS (SELECT 1
 37            FROM ac02
 38           WHERE AAC001 = A.AAC001
 39             and aae140 = '11'
 40             AND AAE036 < date '2018-1-1');
 
Explained.

Elapsed: 00:00:00.36

SQL> select * from table (dbms_xplan.display);


PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------------
| Id  | Operation                         | Name               | Rows  | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT                  |                    |     1 |   202 |       | 11172   (2)|
|   1 |  NESTED LOOPS SEMI                |                    |     1 |   202 |       | 11172   (2)|
|   2 |   NESTED LOOPS ANTI               |                    |     1 |   175 |       | 11168   (2)|
|   3 |    NESTED LOOPS SEMI              |                    |     1 |   150 |       | 11164   (2)|
|   4 |     NESTED LOOPS ANTI             |                    |     1 |   126 |       | 11160   (2)|
|   5 |      NESTED LOOPS SEMI            |                    |     1 |   104 |       | 11158   (2)|
|   6 |       NESTED LOOPS ANTI           |                    |     1 |    67 |       | 11145   (2)|
|   7 |        HASH JOIN ANTI             |                    |     1 |    50 |  8640K| 11143   (2)|
|   8 |         TABLE ACCESS FULL         | AC01_AC02          |   245K|  5755K|       |   356   (2)|
|   9 |         TABLE ACCESS FULL         | AC02               |   559K|    13M|       |  9346   (2)|
|  10 |        TABLE ACCESS BY INDEX ROWID| AB01               |     2 |    34 |       |     2   (0)|
|  11 |         INDEX UNIQUE SCAN         | PK_AB01            |     1 |       |       |     1   (0)|
|  12 |       TABLE ACCESS BY INDEX ROWID | AC13               |   325K|    11M|       |    13   (0)|
|  13 |        INDEX RANGE SCAN           | I_AC13_AAE143      |   446 |       |       |     4   (0)|
|  14 |      INDEX RANGE SCAN             | PK_IC15            |  1771K|    37M|       |     2   (0)|
|  15 |     TABLE ACCESS BY INDEX ROWID   | IC40               |    17M|   395M|       |     4   (0)|
|  16 |      INDEX RANGE SCAN             | PK_IC40            |     1 |       |       |     3   (0)|
|  17 |    TABLE ACCESS BY INDEX ROWID    | AC13               |    51M|  1236M|       |     4   (0)|
|  18 |     INDEX RANGE SCAN              | RELATION_233112_FK |     3 |       |       |     3   (0)|
|  19 |   TABLE ACCESS BY INDEX ROWID     | AC13               |    52M|  1350M|       |     4   (0)|
|  20 |    INDEX RANGE SCAN               | RELATION_233112_FK |     3 |       |       |     3   (0)|
-----------------------------------------------------------------------------------------------------

这条sql,在一个10.2.0.3的系统中执行了十几个小时无法出结果,开发商反馈,该大部分客户的11.2的环境中,大概十几分钟出结果.从来没有遇到此类情况.让我们给他优化sql.看到这个sql,第一反应就是很可能大量的NESTED LOOPS效率低下,怀疑统计信息错误,结果收集完统计信息之后,执行计划依旧,我就在思考怎么调整sql,让其不这样大量嵌套执行.想起来的_unnest_subquery是控制子查询嵌套转换的,从9i开始默认为true,尝试设置为false测试.

SQL> alter session set "_unnest_subquery"=false;

Session altered.

Elapsed: 00:00:00.00
SQL> explain plan for   select 
  2   a.aab034, a.aac001
  3    from si_dp.ac01_ac02 a
  4   where exists (select 1
  5            from ic40
  6           where aac001 = a.aac001
  7             and aae045 <= '201803'
  8             and aae120 = '0')
  9     and not exists (select 1
 10            from ic15
 11           where aac001 = a.aac001
 12             and aae002 <= '201803')
 13     and not EXISTS (select aab001
 14            from ab01
 15           where aab019 in ('91', '93')
 16             AND aab001 = a.aab001)
 17    and exists (select 1
 18            from ac13
 19          where aac001 = a.aac001
 20             and aae140 = '11'
 21             and aae114 in ('0', '1')
 22             and aae002 <= '201803')
 23     AND EXISTS (SELECT 1
 24            FROM AC13
 25           WHERE AAC001 = A.AAC001
 26             and aae140 = '11'
 27             AND AAE143 = '02'
 28             AND AAE003 < '201707'
 29             AND AAE002 BETWEEN '201801' AND '201803'
 30             and aae114 = '1')
 31     AND not EXISTS (SELECT 1
 32            FROM AC13
 33           WHERE AAC001 = A.AAC001
 34             and aae140 = '11'
 35             AND AAE002 < '201801')
 36     AND not EXISTS (SELECT 1
 37            FROM ac02
 38           WHERE AAC001 = A.AAC001
 39             and aae140 = '11'
 40             AND AAE036 < date '2018-1-1');
Explained.

Elapsed: 00:00:00.07

SQL> select * from table (dbms_xplan.display);


PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------------------------

-----------------------------------------------------------------------------------------------
| Id  | Operation                     | Name             | Rows  | Bytes |TempSpc| Cost (%CPU)|
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |                  |   185K|    19M|       |  2991K  (2)|
|   1 |  FILTER                       |                  |       |       |       |            |
|   2 |   HASH JOIN RIGHT SEMI        |                  |   185K|    19M|    16M|   758K  (3)|
|   3 |    TABLE ACCESS BY INDEX ROWID| AC13             |   353K|    12M|       |  4556   (1)|
|   4 |     INDEX SKIP SCAN           | I_AC13_AAB001    | 23608 |       |       |  2287   (1)|
|   5 |    HASH JOIN SEMI             |                  |   201K|    14M|    11M|   751K  (3)|
|   6 |     HASH JOIN SEMI            |                  |   201K|  9452K|  8640K|   123K  (3)|
|   7 |      TABLE ACCESS FULL        | AC01_AC02        |   245K|  5755K|       |   357   (2)|
|   8 |      TABLE ACCESS FULL        | IC40             |    21M|   481M|       | 86122   (3)|
|   9 |     TABLE ACCESS FULL         | AC13             |    52M|  1350M|       |   530K  (3)|
|  10 |   INDEX RANGE SCAN            | PK_IC15          |     2 |    44 |       |     3   (0)|
|  11 |   VIEW                        | index$_join$_009 |     1 |    17 |       |     3  (34)|
|  12 |    HASH JOIN                  |                  |       |       |       |            |
|  13 |     INDEX RANGE SCAN          | PK_AB01          |     1 |    17 |       |     2   (0)|
|  14 |     INLIST ITERATOR           |                  |       |       |       |            |
|  15 |      INDEX RANGE SCAN         | IDX_AB01_AAB019  |     1 |    17 |       |     8   (0)|
|  16 |   TABLE ACCESS BY INDEX ROWID | AC13             |     2 |    50 |       |     5   (0)|
|  17 |    INDEX RANGE SCAN           | I_AC13_SEARCH    |   152 |       |       |     4   (0)|
|  18 |   TABLE ACCESS BY INDEX ROWID | AC02             |     1 |    26 |       |     4   (0)|
|  19 |    INDEX RANGE SCAN           | PK_AC02          |     1 |       |       |     3   (0)|
-----------------------------------------------------------------------------------------------

让开发设置该参数,然后执行sql,结果3分钟不到出结果,非常圆满完成任务.该sql还有进一步优化空间,但是考虑到已经满足要求,不再折腾.

发表在 Oracle性能优化 | 标签为 | 评论关闭

ORA-19821故障分析

发表于 2018 年 5 月 7 日 由 惜分飞

数据库报错
数据库启动报ORA-00283和ORA-19821错

SQL> recover database;
ORA-00283: recovery session canceled due to errors
ORA-19821: an intentionally corrupt log file was found


SQL> recover datafile 1;
ORA-00283: recovery session canceled due to errors
ORA-19821: an intentionally corrupt log file was found

Thu May 03 12:06:51 2018
Recovery of Online Redo Log: Thread 1 Group 1 Seq 1 Reading mem 0
  Mem# 0: D:\APP\SOHTDB\ORADATA\xifenfei\REDO01.LOG
Media Recovery failed with error 19821
Errors in file d:\app\sohtdb\diag\rdbms\xifenfei\xifenfei\trace\xifenfei_pr00_660.trc:
ORA-00283: recovery session canceled due to errors
ORA-19821: an intentionally corrupt log file was found
Slave exiting with ORA-283 exception
Errors in file d:\app\sohtdb\diag\rdbms\xifenfei\xifenfei\trace\xifenfei_pr00_660.trc:
ORA-00283: recovery session canceled due to errors
ORA-19821: an intentionally corrupt log file was found
ORA-283 signalled during: ALTER DATABASE RECOVER  database  ...

ORA-19821报错原因
这个错误相对比较少见，查询mos，由于设置了_disable_logging = TRUE导致该问题
ORA-19821

检查alert日志,_disable_logging参数确实被认为设置为true了.
_disable_logging
解决方法
根据官方的描述,这样的情况无法常规恢复,但是我们知道设置这个参数是为了不产生日志,因此出现这种情况,只能通过隐含参数,禁止数据库进行实例恢复,强制打开数据库.在这样的过程中非常容易遭遇类似ORA-600 2662的错误.
_disable_logging_mos
设置这个参数是为了不产生日志，当数据库非干净关闭(主机断电，数据库crash，shutdown abort等）,就非常可能导致数据库无法正常启动.***千不可万不能在生产环境中设置_disable_logging = TRUE***
参考文档:Ora-19821 during the recovery (Doc ID 1217143.1)
Init.ora Parameter “_DISABLE_LOGGING” [Hidden] Reference Note (Doc ID 29552.1)

发表在 ORA-xxxxx, Oracle备份恢复 | 标签为 , | 评论关闭

Oracle 数据文件大小为0kb或者文件丢失恢复

发表于 2018 年 5 月 6 日 由 惜分飞

接到一个朋友恢复请求,由于rose频繁切换导致文件系统部分数据文件变化为0kb和文件丢失.
故障现象
部分数据文件变化为0kb和文件丢失.
file_lost
file_size_0

这里比较明显,数据库的users03变为了0kb和users04丢失.数据库alert日志报错信息如下:

Completed: alter database mount exclusive
alter database open
Errors in file E:\APP\ADMINISTRATOR\diag\rdbms\orcl\orcl\trace\orcl_dbw0_12008.trc:
ORA-01157: ????/?????? 7 - ??? DBWR ????
ORA-01110: ???? 7: 'E:\APP\ADMINISTRATOR\ORADATA\ORCL\USERS03.DBF'
ORA-27047: ??????????
OSD-04006: ReadFile() 失败, 无法读取文件
O/S-Error: (OS 38) 已到文件结尾。
Errors in file E:\APP\ADMINISTRATOR\diag\rdbms\orcl\orcl\trace\orcl_dbw0_12008.trc:
ORA-01157: ????/?????? 8 - ??? DBWR ????
ORA-01110: ???? 8: 'E:\APP\ADMINISTRATOR\ORADATA\ORCL\USERS04.DBF'
ORA-27041: ??????
OSD-04002: 无法打开文件
O/S-Error: (OS 2) 系统找不到指定的文件。
Errors in file E:\APP\ADMINISTRATOR\diag\rdbms\orcl\orcl\trace\orcl_ora_12040.trc:
ORA-01157: ????/?????? 7 - ??? DBWR ????
ORA-01110: ???? 7: 'E:\APP\ADMINISTRATOR\ORADATA\ORCL\USERS03.DBF'
ORA-1157 signalled during: alter database open...
Fri May 04 09:35:10 2018
Checker run found 2 new persistent data failures

alert日志的报错也比较明显,users03是文件超过了大小(大小为0kb,读取之后肯定超过大小),users04提示无法打开文件(文件在文件系统层面已经丢失).现在问题比较明显由于文件系统故障导致文件大小为0和丢失

碎片扫描恢复
常规的方法肯定无法恢复,比较好的方法只能是底层碎片扫描重组,结合多种扫描工具,最后发现一个做底层恢复的朋友的工具效果不错,扫描结果如下
file_scan

通过工具分析坏块情况

C:\Users\Administrator>dbv FiLe=D:\0504\ORCL_TS.4_FILE.7_10.ora

DBVERIFY: Release 11.2.0.4.0 - Production on 星期六 5月 5 08:52:53 2018

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

DBVERIFY - 开始验证: FILE = D:\0504\ORCL_TS.4_FILE.7_10.ora

………………

页 382565 标记为损坏
Corrupt block relative dba: 0x01c5d665 (file 7, block 382565)
Completely zero block found during dbv:

页 382566 标记为损坏
Corrupt block relative dba: 0x01c5d666 (file 7, block 382566)
Completely zero block found during dbv:

页 382567 标记为损坏
Corrupt block relative dba: 0x01c5d667 (file 7, block 382567)
Completely zero block found during dbv:



DBVERIFY - 验证完成

检查的页总数: 1374720
处理的页总数 (数据): 27582
失败的页总数 (数据): 0
处理的页总数 (索引): 20114
失败的页总数 (索引): 0
处理的页总数 (其他): 1319752
处理的总页数 (段)  : 0
失败的总页数 (段)  : 0
空的页总数: 1
标记为损坏的总页数: 7271
流入的页总数: 0
加密的总页数        : 0
最高块 SCN            : 228271996 (0.228271996)


C:\Users\Administrator>dbv FiLe=D:\0504\ORCL_TS.4_FILE.8_8.ora

DBVERIFY: Release 11.2.0.4.0 - Production on 星期六 5月 5 08:52:53 2018

Copyright (c) 1982, 2011, Oracle and/or its affiliates.  All rights reserved.

DBVERIFY - 开始验证: FILE = D:\0504\ORCL_TS.4_FILE.8_8.ora


DBVERIFY - 验证完成

检查的页总数: 1136896
处理的页总数 (数据): 36639
失败的页总数 (数据): 0
处理的页总数 (索引): 57038
失败的页总数 (索引): 0
处理的页总数 (其他): 1043218
处理的总页数 (段)  : 0
失败的总页数 (段)  : 0
空的页总数: 1
标记为损坏的总页数: 0
流入的页总数: 0
加密的总页数        : 0
最高块 SCN            : 228271997 (0.228271997)

C:\Users\Administrator>

scan_resulte

这里通过分析恢复的两个文件总的block数量2511618，其中连续损坏7271个block损坏,由于出现问题之后,数据库被offline这两个文件继续启动运行了几个小时,导致少量block被覆盖,恢复软件直接置空.后续的恢复比较顺利,正常open数据库,然后处理坏块对象(正好不是业务核心表的lob字段,所有部分丢失影响不是非常大).

温馨提醒:
1. 数据文件和备份不要放在同一个阵列上,更不能是同一个分区（卷）上
2. 出现此类问题之后,应当理解停止对该分区的任何写操作,方式丢失或者大小为0KB的文件被覆盖.
如果需要专业ORACLE数据库恢复技术支持，请联系我们
Phone:17813235971    Q Q:107644445QQ咨询惜分飞    E-Mail:dba@xifenfei.com

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