月归档：四月 2012

DB2备份恢复(全备与恢复)

发表于 2012 年 4 月 22 日 由 惜分飞

日志模式

[db2inst1@xifenfei ~]$ db2 get db cfg for xff |grep -i log
 Log retain for recovery status                          = NO
 User exit for logging status                            = YES   --(1)
 Catalog cache size (4KB)              (CATALOGCACHE_SZ) = 260
 Log buffer size (4KB)                        (LOGBUFSZ) = 98
 Log file size (4KB)                         (LOGFILSIZ) = 1024
 Number of primary log files                (LOGPRIMARY) = 6
 Number of secondary log files               (LOGSECOND) = 4
 Changed path to log files                  (NEWLOGPATH) = 
 Path to log files                                       = /home/db2inst1/xff/redolog/NODE0000/
 Overflow log path                     (OVERFLOWLOGPATH) = 
 Mirror log path                         (MIRRORLOGPATH) = 
 First active log file                                   = S0000013.LOG
 Block log on disk full                (BLK_LOG_DSK_FUL) = NO
 Block non logged operations            (BLOCKNONLOGGED) = NO
 Percent max primary log space by transaction  (MAX_LOG) = 0
 Num. of active log files for 1 active UOW(NUM_LOG_SPAN) = 0
 Percent log file reclaimed before soft chckpt (SOFTMAX) = 520
 Log retain for recovery enabled             (LOGRETAIN) = OFF
 User exit for logging enabled                (USEREXIT) = OFF
 HADR log write synchronization mode     (HADR_SYNCMODE) = NEARSYNC
 First log archive method                 (LOGARCHMETH1) = DISK:/home/db2inst1/xff/archivelog/  --(2)
 Options for logarchmeth1                  (LOGARCHOPT1) = 
 Second log archive method                (LOGARCHMETH2) = OFF
 Options for logarchmeth2                  (LOGARCHOPT2) = 
 Failover log archive path                (FAILARCHPATH) = 
 Number of log archive retries on error   (NUMARCHRETRY) = 5
 Log archive retry Delay (secs)         (ARCHRETRYDELAY) = 20
 Log pages during index build            (LOGINDEXBUILD) = OFF

由(1)和(2)可以判断该数据库处于归档日志模式下

查看当前存在备份

[db2inst1@xifenfei ~]$ db2 list history backup all for xff

                    List History File for xff

Number of matching file entries = 1


 Op Obj Timestamp+Sequence Type Dev Earliest Log Current Log  Backup ID
 -- --- ------------------ ---- --- ------------ ------------ --------------
  B  D  20120406053431001   F    D  S0000000.LOG S0000000.LOG  
 ----------------------------------------------------------------------------
  Contains 2 tablespace(s):

 00001 SYSCATSPACE
 00002 USERSPACE1
 ----------------------------------------------------------------------------
    Comment: DB2 BACKUP XFF OFFLINE    --离线备份
 Start Time: 20120406053431
   End Time: 20120406053439
     Status: A
 ----------------------------------------------------------------------------
  EID: 1 Location: /tmp

在线全备

[db2inst1@xifenfei ~]$ db2 backup db xff online to /tmp  include logs

Backup successful. The timestamp for this backup image is : 20120411165312

[db2inst1@xifenfei ~]$ db2 list history backup all for xff

                    List History File for xff

Number of matching file entries = 2


 Op Obj Timestamp+Sequence Type Dev Earliest Log Current Log  Backup ID
 -- --- ------------------ ---- --- ------------ ------------ --------------
  B  D  20120406053431001   F    D  S0000000.LOG S0000000.LOG  
 ----------------------------------------------------------------------------
  Contains 2 tablespace(s):

 00001 SYSCATSPACE
 00002 USERSPACE1
 ----------------------------------------------------------------------------
    Comment: DB2 BACKUP XFF OFFLINE  --本次试验的online备份
 Start Time: 20120406053431
   End Time: 20120406053439
     Status: A
 ----------------------------------------------------------------------------
  EID: 1 Location: /tmp


 Op Obj Timestamp+Sequence Type Dev Earliest Log Current Log  Backup ID
 -- --- ------------------ ---- --- ------------ ------------ --------------
  B  D  20120411165312001   N    D  S0000013.LOG S0000013.LOG  
 ----------------------------------------------------------------------------
  Contains 3 tablespace(s):

 00001 SYSCATSPACE
 00002 USERSPACE1
 00003 SYSTOOLSPACE
 ----------------------------------------------------------------------------
    Comment: DB2 BACKUP XFF ONLINE
 Start Time: 20120411165312
   End Time: 20120411165322
     Status: A
 ----------------------------------------------------------------------------
  EID: 19 Location: /tmp

当前数据库当前数据

[db2inst1@xifenfei ~]$ db2 connect to xff

   Database Connection Information

 Database server        = DB2/LINUX 9.5.9
 SQL authorization ID   = DB2INST1
 Local database alias   = XFF

[db2inst1@xifenfei ~]$ db2 list tables

Table/View                      Schema          Type  Creation time             
------------------------------- --------------- ----- --------------------------
T_XFF                           DB2INST1        T     2012-04-05-09.45.29.148434
T_XIFENFEI                      DB2INST1        T     2012-04-06-05.50.11.111469

  2 record(s) selected.

[db2inst1@xifenfei ~]$ db2 "create table t_xifenfei01 like t_xff"
DB20000I  The SQL command completed successfully.
[db2inst1@xifenfei ~]$ db2 "insert into t_xifenfei01 
> select * from t_xff"
DB20000I  The SQL command completed successfully.
[db2inst1@xifenfei ~]$ db2 "insert into t_xifenfei01 
select * from t_xff"
DB20000I  The SQL command completed successfully.
[db2inst1@xifenfei ~]$ db2 "select count(*) from t_xifenfei01"

1          
-----------
        734

  1 record(s) selected.

恢复数据库

[db2inst1@xifenfei ~]$ db2 restore db xff from /tmp taken at 20120411165312
SQL2539W  Warning!  Restoring to an existing database that is the same as the 
backup image database.  The database files will be deleted.
Do you want to continue ? (y/n) y
DB20000I  The RESTORE DATABASE command completed successfully.
[db2inst1@xifenfei ~]$ db2 "rollforward db xff to end of logs and stop"

                                 Rollforward Status

 Input database alias                   = xff
 Number of nodes have returned status   = 1

 Node number                            = 0
 Rollforward status                     = not pending
 Next log file to be read               =
 Log files processed                    = S0000013.LOG - S0000014.LOG
 Last committed transaction             = 2012-04-11-08.56.20.000000 UTC

DB20000I  The ROLLFORWARD command completed successfully.
[db2inst1@xifenfei ~]$ db connect to xff
-bash: db: command not found
[db2inst1@xifenfei ~]$ db2 connect to xff

   Database Connection Information

 Database server        = DB2/LINUX 9.5.9
 SQL authorization ID   = DB2INST1
 Local database alias   = XFF

[db2inst1@xifenfei ~]$ db2 list tables

Table/View                      Schema          Type  Creation time             
------------------------------- --------------- ----- --------------------------
T_XFF                           DB2INST1        T     2012-04-05-09.45.29.148434
T_XIFENFEI                      DB2INST1        T     2012-04-06-05.50.11.111469
T_XIFENFEI01                    DB2INST1        T     2012-04-11-16.55.51.853649

  3 record(s) selected.

[db2inst1@xifenfei ~]$ db2 "select count(*) from t_xifenfei01"

1          
-----------
        734

  1 record(s) selected.

备份恢复是dba最重要的职责,本篇做为db2学习过程中第一篇关于备份恢复文章,后续将继续学习db2增量备份恢复等知识.

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OER 7451 in Load Indicator : Error Code = OSD-04500:指定了非法选项

发表于 2012 年 4 月 22 日 由 惜分飞

alert 日志错误
OER 7451 in Load Indicator : Error Code = OSD-04500:指定了非法选项

Sun Apr 22 11:15:51 2012
OER 7451 in Load Indicator : Error Code = OSD-04500: 指定了非法选项
O/S-Error: (OS 1) 函数不正确。 !
OER 7451 in Load Indicator : Error Code = OSD-04500: 指定了非法选项
O/S-Error: (OS 1) 函数不正确。 !
Sun Apr 22 11:16:01 2012
OER 7451 in Load Indicator : Error Code = OSD-04500: 指定了非法选项
O/S-Error: (OS 1) 函数不正确。 !
OER 7451 in Load Indicator : Error Code = OSD-04500: 指定了非法选项
O/S-Error: (OS 1) 函数不正确。 !
Sun Apr 22 11:16:11 2012
OER 7451 in Load Indicator : Error Code = OSD-04500: 指定了非法选项
O/S-Error: (OS 1) 函数不正确。 !

错误信息说明

07451, 00000, "slskstat: unable to obtain load information."
// *Cause:  kstat library returned an error. Possible OS failure
// *Action: Check result code in sercose[0] for more information.

数据库版本信息

SQL> select * from v$version;

BANNER
------------------------------------------------------------------------

Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - Production  <<== 32位数据库
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for 32-bit Windows: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production

操作系统信息

C:\Users\XIFENFEI>systeminfo
主机名:           XIFENFEI-PC
OS 名称:          Microsoft Windows 7 旗舰版 
OS 版本:          6.1.7601 Service Pack 1 Build 7601
OS 制造商:        Microsoft Corporation
OS 配置:          独立工作站
OS 构件类型:      Multiprocessor Free
注册的所有人:     XIFENFEI
注册的组织:       Microsoft
产品 ID:          00426-068-8452196-86428
初始安装日期:     2012/2/28, 20:37:08
系统启动时间:     2012/4/22, 9:16:07
系统制造商:       Dell Inc.
系统型号:         Inspiron N4050
系统类型:         x64-based PC       <<==操心系统是win 7 64位
处理器:           安装了 1 个处理器。
                  [01]: Intel64 Family 6 Model 42 Stepping 7 GenuineIntel ~2300 Mhz
BIOS 版本:        Dell Inc. A06, 2011/11/14
Windows 目录:     C:\Windows
系统目录:         C:\Windows\system32
启动设备:         \Device\HarddiskVolume1
系统区域设置:     zh-cn;中文(中国)
输入法区域设置:   zh-cn;中文(中国)
时区:             (UTC+08:00)北京，重庆，香港特别行政区，乌鲁木齐
物理内存总量:     8,100 MB
可用的物理内存:   5,196 MB
虚拟内存: 最大值: 9,122 MB
虚拟内存: 可用:   5,315 MB
虚拟内存: 使用中: 3,807 MB
页面文件位置:     D:\pagefile.sys
域:               WORKGROUP
登录服务器:       \\XIFENFEI-PC

错误原因

Installed 32-bit Oracle database software on a 64-bit MS Windows OS which is not supported.

Note: For the Database software, you can ONLY install the x64 version on MS Windows (x64).
          You can NOT install the 32-bit version Database software on MS Windows (x64).

解决办法

Install 32-bit Oracle database software only on 32-bit MS Windows OS.
发表在 ORA-xxxxx | 标签为 , | 一条评论

执行计划中常见index访问方式

发表于 2012 年 4 月 21 日 由 惜分飞

近期有朋友对于单个表上的index各种情况比较模糊,这里对于单个表上,单个index出现的大多数情况进行了总结性测试,给出了测试结果,至于为什么出现这样的试验结果未做过多解释,给读者留下思考的空间.本篇文章仅仅是为了测试hint对index的影响,而不是说明走各种index方式的好坏.参考: INDEX FULL SCAN vs INDEX FAST FULL SCAN
创建表模拟测试

SQL> create table t_xifenfei as select object_id,object_name from dba_objects;

Table created.


SQL>  create index i_t_object_id on t_xifenfei(object_id); 

Index created.

SQL> exec dbms_stats.gather_table_stats(USER,'T_XIFENFEI',cascade=>true); 

PL/SQL procedure successfully completed.

SQL> desc t_xifenfei
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 OBJECT_ID                                          NUMBER
 OBJECT_NAME                                        VARCHAR2(128)

TABLE ACCESS FULL

SQL> SET AUTOT TRACE EXP STAT
SQL> SELECT OBJECT_ID FROM T_XIFENFEI;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 548923532

--------------------------------------------------------------------------------
| Id  | Operation         | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |            | 49838 |   243K|    57   (2)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T_XIFENFEI | 49838 |   243K|    57   (2)| 00:00:01 |
--------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3544  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

SQL> SELECT /*+ INDEX(T i_t_object_id) */ OBJECT_ID FROM T_XIFENFEI;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 548923532

--------------------------------------------------------------------------------
| Id  | Operation         | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT  |            | 49838 |   243K|    57   (2)| 00:00:01 |
|   1 |  TABLE ACCESS FULL| T_XIFENFEI | 49838 |   243K|    57   (2)| 00:00:01 |
--------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3544  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

从上面的执行计划中可知,此时走了全表扫描. 由于我们需要查询的列为object_id,因此理论上只需要读取索引就应该可以返回所有数据,而此时为什么是全表扫描呢？ 这是因为NULL值与索引的特性所决定的.即null值不会被存储到B树索引.因此应该为表 t_xifenfei 的列 object_id 添加 not null 约束.

INDEX FAST FULL SCAN

SQL> alter table t_xifenfei modify(object_id not null);   

Table altered.

SQL> SELECT  object_id from t_xifenfei;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2036340805

--------------------------------------------------------------------------------------
| Id  | Operation            | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |               | 49838 |   243K|    27   (4)| 00:00:01 |
|   1 |  INDEX FAST FULL SCAN| I_T_OBJECT_ID | 49838 |   243K|    27   (4)| 00:00:01 |
--------------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3432  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

INDEX FAST FULL SCAN:当在高速缓存中没有找到所需的索引块时,则根据db_file_multiblock_read_count的值进行多块读操作.对于索引的分支结构只是简单的获取,然后扫描所有的叶结点.其结果是导致索引结构没有访问,获取的数据没有根据索引键的顺序排序.INDEX FAST FULL SCAN使用multiblock_read,故产生db file scattered reads 事件.

INDEX RANGE SCAN

SQL> select object_id from t_xifenfei where object_id<10;

8 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2197008162

----------------------------------------------------------------------------------
| Id  | Operation        | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |               |     2 |    10 |     2   (0)| 00:00:01 |
|*  1 |  INDEX RANGE SCAN| I_T_OBJECT_ID |     2 |    10 |     2   (0)| 00:00:01 |
----------------------------------------------------------------------------------

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

   1 - access("OBJECT_ID"<10)


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          3  consistent gets
          0  physical reads
          0  redo size
        499  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          8  rows processed

SQL> select /*+ index_ffs(t i_t_object_id) */ object_id from t_xifenfei t where object_id<10;

8 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2036340805

--------------------------------------------------------------------------------------
| Id  | Operation            | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT     |               |     2 |    10 |    27   (4)| 00:00:01 |
|*  1 |  INDEX FAST FULL SCAN| I_T_OBJECT_ID |     2 |    10 |    27   (4)| 00:00:01 |
--------------------------------------------------------------------------------------

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

   1 - filter("OBJECT_ID"<10)


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        118  consistent gets
          0  physical reads
          0  redo size
        499  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          8  rows processed
1
这里可以看出index_ffs已经生效,但是对于这样的情况hint index_ffs效率一般来说不会太高.
<br>
<strong>INDEX FULL SCAN</strong>
1
SQL> SELECT /*+ INDEX(T i_t_object_id) */ object_id  from t_xifenfei t;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 431110666

----------------------------------------------------------------------------------
| Id  | Operation        | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |               | 49838 |   243K|   113   (2)| 00:00:02 |
|   1 |  INDEX FULL SCAN | I_T_OBJECT_ID | 49838 |   243K|   113   (2)| 00:00:02 |
----------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3426  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

INDEX FULL SCAN:完全按照索引存储的顺序依次访问整个索引树.当访问到叶结点之后,按照双向链表方式读取相连节点的值.换言之,对于索引上所有的数据是按照有序的方式来读取的.如果索引块没有在高速缓存中被找到时,则需要从数据文件中单块进行读取.对于需要读取大量数据的全索引扫描而言,这将使其变得低效.INDEX FULL SCAN使用single read,故产生db file sequential reads事件.新版的Oracle支持db file parallel reads方式.
HINT INDEX不会使用INDEX FAST FULL SCAN功能.

INDEX列ORDER BY

SQL> SELECT OBJECT_ID FROM T_XIFENFEI order by object_id ;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 431110666

----------------------------------------------------------------------------------
| Id  | Operation        | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT |               | 49838 |   243K|   113   (2)| 00:00:02 |
|   1 |  INDEX FULL SCAN | I_T_OBJECT_ID | 49838 |   243K|   113   (2)| 00:00:02 |
----------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3426  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

SQL> SELECT OBJECT_ID FROM T_XIFENFEI order by object_id  desc;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2808014233

--------------------------------------------------------------------------------------------
| Id  | Operation                  | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |               | 49838 |   243K|   113   (2)| 00:00:02 |
|   1 |  INDEX FULL SCAN DESCENDING| I_T_OBJECT_ID | 49838 |   243K|   113   (2)| 00:00:02 |
--------------------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
       3427  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
      49838  rows processed

SQL> SELECT  /*+ index_ffs(t i_t_object_id) */ object_id from t_xifenfei t order by object_id;

49838 rows selected.


Execution Plan
----------------------------------------------------------
Plan hash value: 2527678987

-----------------------------------------------------------------------------------------------
| Id  | Operation             | Name          | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |               | 49838 |   243K|       |   185   (4)| 00:00:03 |
|   1 |  SORT ORDER BY        |               | 49838 |   243K|  1192K|   185   (4)| 00:00:03 |
|   2 |   INDEX FAST FULL SCAN| I_T_OBJECT_ID | 49838 |   243K|       |    27   (4)| 00:00:01 |
-----------------------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        117  consistent gets
          0  physical reads
          0  redo size
     721203  bytes sent via SQL*Net to client
      36927  bytes received via SQL*Net from client
       3324  SQL*Net roundtrips to/from client
          1  sorts (memory)
          0  sorts (disk)
      49838  rows processed

对于index 列排序,默认情况下会使用INDEX FULL SCAN/INDEX FULL SCAN DESCENDING而不选择使用INDEX FAST FULL SCAN,因为INDEX FAST FULL SCAN获得数据后,还需要做一次SORT ORDER BY操作

INDEX FAST FULL SCAN+SORT AGGREGATE

SQL> SELECT  count(object_id) FROM T_XIFENFEI;


Execution Plan
----------------------------------------------------------
Plan hash value: 3095383276

-------------------------------------------------------------------------------
| Id  | Operation             | Name          | Rows  | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------
|   0 | SELECT STATEMENT      |               |     1 |    27   (4)| 00:00:01 |
|   1 |  SORT AGGREGATE       |               |     1 |            |          |
|   2 |   INDEX FAST FULL SCAN| I_T_OBJECT_ID | 49838 |    27   (4)| 00:00:01 |
-------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        117  consistent gets
          0  physical reads
          0  redo size
        421  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL> SELECT  /*+ INDEX(T i_t_object_id) */ count(object_id) FROM T_XIFENFEI t;


Execution Plan
----------------------------------------------------------
Plan hash value: 3079973526

--------------------------------------------------------------------------
| Id  | Operation        | Name          | Rows  | Cost (%CPU)| Time     |
--------------------------------------------------------------------------
|   0 | SELECT STATEMENT |               |     1 |   113   (2)| 00:00:02 |
|   1 |  SORT AGGREGATE  |               |     1 |            |          |
|   2 |   INDEX FULL SCAN| I_T_OBJECT_ID | 49838 |   113   (2)| 00:00:02 |
--------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
        111  consistent gets
          0  physical reads
          0  redo size
        421  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

sort aggregate通常发生在使用一些聚合函数的时候,sum(),avg(),min(),max(),count()等等,实际上sort aggregate不做真正的sort,并不会用到排序空间,而是通过一个全局变量＋全表或全索引扫描来实现.这样的操作在默认情况下使用INDEX FAST FULL SCAN

INDEX FULL SCAN (MIN/MAX)

SQL> SELECT  max(object_id) FROM T_XIFENFEI;


Execution Plan
----------------------------------------------------------
Plan hash value: 2939893782

--------------------------------------------------------------------------------------------
| Id  | Operation                  | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |               |     1 |     5 |     2   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE            |               |     1 |     5 |            |          |
|   2 |   INDEX FULL SCAN (MIN/MAX)| I_T_OBJECT_ID | 49838 |   243K|     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        419  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

SQL>  SELECT /*+ index_ffs(t i_t_object_id) */ max(object_id) FROM T_XIFENFEI t;


Execution Plan
----------------------------------------------------------
Plan hash value: 2939893782

--------------------------------------------------------------------------------------------
| Id  | Operation                  | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT           |               |     1 |     5 |    27   (4)| 00:00:01 |
|   1 |  SORT AGGREGATE            |               |     1 |     5 |            |          |
|   2 |   INDEX FULL SCAN (MIN/MAX)| I_T_OBJECT_ID | 49838 |   243K|    27   (4)| 00:00:01 |
--------------------------------------------------------------------------------------------


Statistics
----------------------------------------------------------
          1  recursive calls
          0  db block gets
          2  consistent gets
          0  physical reads
          0  redo size
        419  bytes sent via SQL*Net to client
        385  bytes received via SQL*Net from client
          2  SQL*Net roundtrips to/from client
          0  sorts (memory)
          0  sorts (disk)
          1  rows processed

对于这样的查询INDEX FULL SCAN (MIN/MAX)明显是最优,但是此处奇怪的是使用了index_ffs提示无效,如果有知道的朋友,麻烦告知原因.

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