分类目录归档：Oracle

DBMS_STATS比较复杂参数

发表于 2011 年 9 月 4 日由惜分飞

method_opt
Accepts:
FOR ALL [INDEXED | HIDDEN] COLUMNS [size_clause]
FOR COLUMNS [size clause] column|attribute [size_clause] [,column|attribute [size_clause]…]
size_clause is defined as size_clause := SIZE {integer | REPEAT | AUTO | SKEWONLY}

- integer : Number of histogram buckets. Must be in the range [1,254].
- REPEAT : Collects histograms only on the columns that already have histograms.
- AUTO : Oracle determines the columns to collect histograms based on data distribution and the workload of the columns.
- SKEWONLY : Oracle determines the columns to collect histograms based on the data distribution of the columns.

举例说明：
method_opt => ‘FOR COLUMNS size 254 object_id’ 收集objct_id列直方图
method_opt => ‘FOR COLUMNS size 1 object_id’ 删除object_id列直方图
method_opt => ‘for all columns size repeat’ 重新分析现有直方图
method_opt => ‘for all columns size auto’ oracle决定收集哪些列的直方图（需要设置table monitoring）
method_opt => ‘for all columns size skewonly’ oracle分析所有列的分布情况，生成直方图
method_opt => ‘FOR COLUMNS object_id size SKEWONLY’ 收集object_id列分布情况，生成直方图
method_opt => ‘FOR all INDEXED COLUMNS size SKEWONLY’ 收集index列分布情况，并生成直方图

granularity
Granularity of statistics to collect (only pertinent if the table is partitioned).
‘ALL’ – gathers all (subpartition, partition, and global) statistics
‘AUTO’- determines the granularity based on the partitioning type. This is the default value.
‘DEFAULT’ – gathers global and partition-level statistics. This option is obsolete, and while currently supported, it is included in the documentation for legacy reasons only. You should use the ‘GLOBAL AND PARTITION’ for this functionality. Note that the default value is now ‘AUTO’.
‘GLOBAL’ – gathers global statistics
‘GLOBAL AND PARTITION’ – gathers the global and partition level statistics. No subpartition level statistics are gathered even if it is a composite partitioned object.
‘PARTITION ‘- gathers partition-level statistics
‘SUBPARTITION’ – gathers subpartition-level statistics.

options
Further specification of which objects to gather statistics for:
GATHER: Gathers statistics on all objects in the schema.
GATHER AUTO: Gathers all necessary statistics automatically. Oracle implicitly determines which objects need new statistics, and determines how to gather those statistics. When GATHER AUTO is specified, the only additional valid parameters are ownname, stattab, statid, objlist and statown; all other parameter settings are ignored. Returns a list of processed objects.
GATHER STALE: Gathers statistics on stale objects as determined by looking at the *_tab_modifications views. Also, return a list of objects found to be stale.
GATHER EMPTY: Gathers statistics on objects which currently have no statistics. also, return a list of objects found to have no statistics.
LIST AUTO: Returns a list of objects to be processed with GATHER AUTO.
LIST STALE: Returns list of stale objects as determined by looking at the *_tab_modifications views.
LIST EMPTY: Returns list of objects which currently have no statistics.

发表在 Oracle性能优化 | 一条评论

BITMAP CONVERSION FROM ROWIDS

发表于 2011 年 9 月 2 日由惜分飞

在有些执行计划中，可以会看到 BITMAP CONVERSION FROM ROWIDS这样的东东，也许你会感觉奇怪，我没有使用位图索引怎么出现了bitmap。
我通过一个sql和大家分析下原因：
sql语句为：

SELECT *
  FROM (SELECT a.*, ROWNUM rn
          FROM (  SELECT module_no, MAX (id) AS id
                    FROM vasoa.tab_moa_historypage t
                   WHERE t.company_id = :1 AND t.user_id = :2 AND t.TYPE = :3
                GROUP BY module_no
                ORDER BY id DESC) a
         WHERE ROWNUM <= :4) b
WHERE b.rn >= :5

执行计划为：

表结构为：

目前索引情况：

通过观察执行计划的图片可以发现，使用了 BITMAP CONVERSION FROM ROWIDS，其目的是：.oracle将btree索引中获得的rowid信息通过BITMAP CONVERSION FROM ROWIDS的步骤转换成bitmap进行匹配,然后匹配完成后通过BITMAP CONVERSION TO ROWIDS再转换出rowid获得数据或者回表获得数据。这种想象出现的原因为：oracle的cbo是根据cost来决定大小来选择合适的执行计划，当它计算获得通过bitmap的方式执行的时候cost会更小，它就会选择使用这样的执行计划。一般出现这样的情况，都是因为对表建立的不适当的index导致，特别是对表中的唯一度不高的列建立了index，然后oracle就有可能选择两个这样的列转为为bitmap来执行。根据oracle的执行计划，肯定是cost最小的，但是它很多时候忽略了一致性读等其他条件，导致这个执行计划并非像oracle想象的那样最优，因为把btree index转为为bitmap index执行，需要消耗更多的cpu，特别是在cpu比较紧张的系统中，所以这样的情况如果发生在oltp系统中，一般都需要解决。
本例的解决办法是删除唯一度低的index，建立组合index。分别删除COMPANY_ID与USER_ID上的index，建立COMPANY_ID和USER_ID的组合index，执行计划如下：

发表在 Oracle性能优化 | 3 条评论

bbed 修改datafile header

发表于 2011 年 8 月 31 日由惜分飞

SQL> startup
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
Database mounted.
ORA-01113: file 2 needs media recovery
ORA-01110: data file 2: '/opt/oracle/oradata/xifenfei/xff01.dbf'
提示数据文件2需要恢复，首选是recover datafile 2;，如果失败，可以考虑bbed修改scn的办法

SQL> select file#,to_char(checkpoint_change#,'999999999999') from v$datafile;

     FILE# TO_CHAR(CHECK
---------- -------------
         1  107374278108
         2  107374278108
         3  107374278108
         4  107374278108
         5  107374278108
         6  107374278108
         7  107374278108
         8  107374278108
         9  107374278108
        10  107374278108
        11  107374278108

11 rows selected.

SQL> select file#,online_status,to_char(change#,'999999999999') from v$recover_file;

     FILE# ONLINE_ TO_CHAR(CHANG
---------- ------- -------------
         2 ONLINE   107374277136

[oracle@localhost tmp]$ bbed parfile=/tmp/parfile.cnf
Password: 

BBED: Release 2.0.0.0.0 - Limited Production on Mon Aug 22 06:05:34 2011

Copyright (c) 1982, 2002, Oracle Corporation.  All rights reserved.

************* !!! For Oracle Internal Use only !!! ***************

BBED> info
 File#  Name                                                        Size(blks)
 -----  ----                                                        ----------
     1  /opt/oracle/oradata/xifenfei/system01.dbf                         1280
     2  /opt/oracle/oradata/xifenfei/xff01.dbf                            1280

BBED> set dba 1,1
        DBA             0x00400001 (4194305 1,1)

BBED> p kcvfhckp
struct kcvfhckp, 36 bytes                   @140     
   struct kcvcpscn, 8 bytes                 @140     
*    ub4 kscnbas                           @140      0x000175dc
      ub2 kscnwrp                           @144      0x0019
* ub4 kcvcptim                             @148      0x2d49fbbb
   ub2 kcvcpthr                             @152      0x0001
   union u, 12 bytes                        @156     
      struct kcvcprba, 12 bytes             @156     
         ub4 kcrbaseq                       @156      0x00000005
         ub4 kcrbabno                       @160      0x00008e05
         ub2 kcrbabof                       @164      0x0010
      struct kcvcptr, 12 bytes              @156     
         struct kcrtrscn, 8 bytes           @156     
            ub4 kscnbas                     @156      0x00000005
            ub2 kscnwrp                     @160      0x8e05
         ub4 kcrtrtim                       @164      0x09110010
   ub1 kcvcpetb[0]                          @168      0x02
   ub1 kcvcpetb[1]                          @169      0x00
   ub1 kcvcpetb[2]                          @170      0x00
   ub1 kcvcpetb[3]                          @171      0x00
   ub1 kcvcpetb[4]                          @172      0x00
   ub1 kcvcpetb[5]                          @173      0x00
   ub1 kcvcpetb[6]                          @174      0x00
   ub1 kcvcpetb[7]                          @175      0x00

BBED> p kcvfhcpc
*ub4 kcvfhcpc                                @176      0x0000007a

BBED> p kcvfhccc
*ub4 kcvfhccc                                @184      0x00000079
星号表示使用bbed修改datafile header scn需要考虑的地方

SQL> select to_char(to_number('19000175dc','xxxxxxxxxxxx'),'999999999999') from dual;

TO_CHAR(TO_NU
-------------
 107374278108
证实system01.dbf的scn为107374278108和v$datafile查询到的一致

BBED> set dba 2,1
        DBA             0x00800001 (8388609 2,1)

BBED> p kcvfhckp
struct kcvfhckp, 36 bytes                   @140     
   struct kcvcpscn, 8 bytes                 @140     
      ub4 kscnbas                           @140      0x00017210
      ub2 kscnwrp                           @144      0x0019
   ub4 kcvcptim                             @148      0x2d49fa27
   ub2 kcvcpthr                             @152      0x0001
   union u, 12 bytes                        @156     
      struct kcvcprba, 12 bytes             @156     
         ub4 kcrbaseq                       @156      0x00000005
         ub4 kcrbabno                       @160      0x00006f18
         ub2 kcrbabof                       @164      0x0010
      struct kcvcptr, 12 bytes              @156     
         struct kcrtrscn, 8 bytes           @156     
            ub4 kscnbas                     @156      0x00000005
            ub2 kscnwrp                     @160      0x6f18
         ub4 kcrtrtim                       @164      0x09110010
   ub1 kcvcpetb[0]                          @168      0x02
   ub1 kcvcpetb[1]                          @169      0x00
   ub1 kcvcpetb[2]                          @170      0x00
   ub1 kcvcpetb[3]                          @171      0x00
   ub1 kcvcpetb[4]                          @172      0x00
   ub1 kcvcpetb[5]                          @173      0x00
   ub1 kcvcpetb[6]                          @174      0x00
   ub1 kcvcpetb[7]                          @175      0x00

BBED> p kcvfhcpc
ub4 kcvfhcpc                                @176      0x00000034

BBED> p kcvfhccc
ub4 kcvfhccc                                @184      0x00000033


SQL> select to_char(to_number('1900017210','xxxxxxxxxxxx'),'999999999999') from dual;

TO_CHAR(TO_NU
-------------
 107374277136
和v$recover_file视图中查询出来一致

BBED> set dba 2,1 offset 140
        DBA             0x00800001 (8388609 2,1)
        OFFSET          140

BBED> show 
        FILE#           2
        BLOCK#          1
        OFFSET          140
        DBA             0x00800001 (8388609 2,1)
        FILENAME        /opt/oracle/oradata/xifenfei/xff01.dbf
        BIFILE          bifile.bbd
        LISTFILE        /tmp/list
        BLOCKSIZE       8192
        MODE            Edit
        EDIT            Unrecoverable
        IBASE           Dec
        OBASE           Dec
        WIDTH           80
        COUNT           32
        LOGFILE         log.bbd
        SPOOL           No

BBED> m /x dc750100
 File: /opt/oracle/oradata/xifenfei/xff01.dbf (2)
 Block: 1                Offsets:  140 to  171           Dba:0x00800001
------------------------------------------------------------------------
 dc750100 19000000 27fa492d 01000000 05000000 186f0000 10001109 02000000 

 <32 bytes per line>

BBED> m /x bbfb492d offset 158
 File: /opt/oracle/oradata/xifenfei/xff01.dbf (2)
 Block: 1                Offsets:  158 to  189           Dba:0x00800001
------------------------------------------------------------------------
 bbfb492d 00001000 11090200 00000000 00003400 00004cc0 492d3300 00000000 

 <32 bytes per line>

BBED> m /x 7a000000 offset 176
 File: /opt/oracle/oradata/xifenfei/xff01.dbf (2)
 Block: 1                Offsets:  176 to  207           Dba:0x00800001
------------------------------------------------------------------------
 7a000000 4cc0492d 33000000 00000000 00000000 00000000 00000000 00000000 

 <32 bytes per line>

BBED> m /x 79000000 offset 184
 File: /opt/oracle/oradata/xifenfei/xff01.dbf (2)
 Block: 1                Offsets:  184 to  215           Dba:0x00800001
------------------------------------------------------------------------
 79000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 

 <32 bytes per line>
注意：p打印出来的值和m修改的值可能不是完全一致（和cpu的计算类型有关，常用的intel cpu中是倒序存储），可以选择先dump正确的相关值，然后m修改
如：p打印出来的值为：80084d1f时，m修改时要为： 1f4d0880

BBED> sum apply dba 2,1
Check value for File 2, Block 1:
current = 0x7ece, required = 0x7ece


SQL> shutdown immediate
ORA-01109: database not open

Database dismounted.
ORACLE instance shut down.
SQL> startup
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
Database mounted.
ORA-01122: database file 2 failed verification check
ORA-01110: data file 2: '/opt/oracle/oradata/xifenfei/xff01.dbf'
ORA-01207: file is more recent than controlfile - old controlfile
提示控制文件太老，需要重建控制文件

SQL> shutdown abort
ORACLE instance shut down.
SQL> STARTUP NOMOUNT
CREATE CONTROLFILE REUSE DATABASE "XIFENFEI" NORESETLOGS  ARCHIVELOG
    MAXLOGFILES 50
    MAXLOGMEMBERS 5
    MAXDATAFILES 100
    MAXINSTANCES 1
    MAXLOGHISTORY 226
LOGFILE
  GROUP 1 '/opt/oracle/oradata/xifenfei/redo01.log'  SIZE 100M,
  GROUP 2 '/opt/oracle/oradata/xifenfei/redo02.log'  SIZE 100M,
  GROUP 3 '/opt/oracle/oradata/xifenfei/redo03.log'  SIZE 100M
DATAFILE
  '/opt/oracle/oradata/xifenfei/system01.dbf',
  '/opt/oracle/oradata/xifenfei/xff01.dbf',
  '/opt/oracle/oradata/xifenfei/cwmlite01.dbf',
  '/opt/oracle/oradata/xifenfei/drsys01.dbf',
  '/opt/oracle/oradata/xifenfei/example01.dbf',
  '/opt/oracle/oradata/xifenfei/indx01.dbf',
  '/opt/oracle/oradata/xifenfei/odm01.dbf',
  '/opt/oracle/oradata/xifenfei/tools01.dbf',
  '/opt/oracle/oradata/xifenfei/users01.dbf',
  '/opt/oracle/oradata/xifenfei/xdb01.dbf',
  '/opt/oracle/oradata/xifenfei/UNDOTBS01.dbf'
CHARACTER SET ZHS16GBK
;
ORACLE instance started.

Total System Global Area  236000356 bytes
Fixed Size                   451684 bytes
Variable Size             201326592 bytes
Database Buffers           33554432 bytes
Redo Buffers                 667648 bytes
SQL>   2    3    4    5    6    7    8    9   10   11   12   13   14   15   16   17   18   19   20   
Control file created.

SQL> alter database open;

Database altered.

SQL> ALTER TABLESPACE TEMP ADD TEMPFILE '/opt/oracle/oradata/xifenfei/temp01.dbf'
  2       SIZE 32505856  REUSE AUTOEXTEND ON NEXT 655360  MAXSIZE 32767M;
重建控制文件后，需要添加临时文件

补充说明：
1、datafile 的file header 存储在第一个block里
2、Oracle considers four attributes of this data structure when determining if a datafile is sync with the other data files of the database:（不同oracle版本offset可能不同）
（1）kscnbas (at offset 140) – SCN of last change to the datafile.
（2）kcvcptim (at offset 148) -Time of the last change to the datafile.
（3）kcvfhcpc (at offset 176) – Checkpoint count.
（4）kcvfhccc (at offset 184) – Unknown, but is always 1 less than thecheckpoint point count.
Oracle有4个属性来判断datafile 是否和其他的datafile 一致，如果都一致，可以正常操作，如果不一致，那么会报ORA-01113错误
使用Oracle Recovery Tools一键式解决给问题

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分类目录归档：Oracle

DBMS_STATS比较复杂参数

BITMAP CONVERSION FROM ROWIDS

bbed 修改datafile header

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分类目录归档：Oracle

DBMS_STATS比较复杂参数

BITMAP CONVERSION FROM ROWIDS

bbed 修改datafile header

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