关于ORACLE通过file_id与block_id定位数据库对象遇到的问题的一点思考

在ORACLE中，我们可以通过file_id（file#）与block_id（block#）去定位一个数据库对象（object）。例如，我们在10046生成的trace文件中file#=4 block#=266 blocks=8,那么我可以通过下面两个SQL去定位对象

SQL 1：此SQL效率较差，执行时间较长。

SELECT OWNER, 

       SEGMENT_NAME, 

       SEGMENT_TYPE, 

       TABLESPACE_NAME 

FROM   DBA_EXTENTS 

WHERE  FILE_ID =&FILE_ID

       AND &BLOCK_ID BETWEEN BLOCK_ID AND BLOCK_ID + BLOCKS - 1;

 

SQL 2：此SQL效率较快（ORACLE 10g 中没有CACHEHINT字段）

SELECT OBJD, 

       FILE#, 

       BLOCK#, 

       CLASS#, 

       TS#, 

       CACHEHINT, 

       STATUS, 

       DIRTY 

FROM   V$BH 

WHERE  FILE# = &FILE_ID 

       AND BLOCK# = &BLOCK_ID; 

SELECT OWNER, OBJECT_NAME FROM DBA_OBJECTS WHERE OBJECT_ID=&OBJECT_ID;

下面通过一个例子来演示一下，详情如下所示

SQL> COL OWNER FOR A12;

SQL> COL SEGMENT_NAME FOR A32;

SQL> SELECT OWNER       ,

  2         SEGMENT_NAME ,

  3         HEADER_FILE  ,

  4         HEADER_BLOCK

  5  FROM DBA_SEGMENTS          

  6  WHERE OWNER='TEST' AND SEGMENT_NAME='EMPLOYEE';

OWNER        SEGMENT_NAME                     HEADER_FILE HEADER_BLOCK

------------ -------------------------------- ----------- ------------

TEST         EMPLOYEE                                   4          266

SQL> 

SQL> SELECT OWNER, 

  2         SEGMENT_NAME, 

  3         SEGMENT_TYPE, 

  4         TABLESPACE_NAME 

  5  FROM   DBA_EXTENTS 

  6  WHERE  FILE_ID = 4 

  7         AND 266 BETWEEN BLOCK_ID AND BLOCK_ID + BLOCKS - 1;

OWNER        SEGMENT_NAME                     SEGMENT_TYPE       TABLESPACE_NAME

------------ -------------------------------- ------------------ -----------------

TEST         EMPLOYEE                         TABLE              USERS

SQL> 

SQL> SELECT OBJD, 

  2         FILE#, 

  3         BLOCK#, 

  4         CLASS#, 

  5         TS#, 

  6         CACHEHINT, 

  7         STATUS, 

  8         DIRTY 

  9  FROM   V$BH 

 10  WHERE  FILE# = 4 

 11         AND BLOCK# = 266; 

      OBJD      FILE#     BLOCK#     CLASS#        TS#  CACHEHINT STATUS     D

---------- ---------- ---------- ---------- ---------- ---------- ---------- -

     76090          4        266          4          4         15 cr         N

     76090          4        266          4          4         15 cr         N

     76090          4        266          4          4         15 cr         N

SQL> SELECT OWNER, OBJECT_NAME FROM DBA_OBJECTS WHERE OBJECT_ID=76090;

OWNER        OBJECT_NAME

------------ ------------------------------------------------------------

TEST         EMPLOYEE

昨天在群里讨论一个关于空闲块的问题时，我验证测试时，发现一个奇怪的现象，使用下面SQL找到了一个最大空闲块。

SELECT UPPER(F.TABLESPACE_NAME)           AS "表空间名",

       D.TOT_GROOTTE_MB                   AS "表空间大小(M)",

       D.TOT_GROOTTE_MB  - F.TOTAL_BYTES  AS "已使用空间(M)",

       TO_CHAR(ROUND((D.TOT_GROOTTE_MB - F.TOTAL_BYTES) / D.TOT_GROOTTE_MB * 100,2),'990.99')

                                          AS "使用比",

       F.TOTAL_BYTES                      AS "空闲空间(M)",

       F.MAX_BYTES                        AS "最大空闲块(M)"

FROM

  (SELECT TABLESPACE_NAME,

    ROUND(SUM(BYTES) / (1024 * 1024), 2) TOTAL_BYTES,

    ROUND(MAX(BYTES) / (1024 * 1024), 2) MAX_BYTES

  FROM SYS.DBA_FREE_SPACE

  GROUP BY TABLESPACE_NAME

  ) F,

  (SELECT DD.TABLESPACE_NAME,

    ROUND(SUM(DD.BYTES) / (1024 * 1024), 2) TOT_GROOTTE_MB

  FROM SYS.DBA_DATA_FILES DD

  GROUP BY DD.TABLESPACE_NAME

  ) D

WHERE D.TABLESPACE_NAME = F.TABLESPACE_NAME;

SELECT FILE_ID,BLOCK_ID, BYTES,BLOCKS 

FROM DBA_FREE_SPACE  

WHERE TABLESPACE_NAME=&TABLESPACE_NAME  

ORDER BY BYTES DESC;

然后我发现使用上面两个SQL查不到对应的对象。如下截图所示：

后面查了一下资料，发现在Oracle Database 10g引入了回收站功能后，会将回收站（RECYCLEBIN$）中的空间计算为自由空间，加入到dba_free_space字典中。在$ORACLE_HOME/rdbms/admin/catspace.sql中，你可以找到视图DBA_FREE_SPACE的定义，脚本如下：

ORACLE 10g中DBA_FREE_SPACE的定义：

create or replace view DBA_FREE_SPACE

    (TABLESPACE_NAME, FILE_ID, BLOCK_ID,

     BYTES, BLOCKS, RELATIVE_FNO)

as

select ts.name, fi.file#, f.block#,

       f.length * ts.blocksize, f.length, f.file#

from sys.ts$ ts, sys.fet$ f, sys.file$ fi

where ts.ts# = f.ts#

  and f.ts# = fi.ts#

  and f.file# = fi.relfile#

  and ts.bitmapped = 0

union all

select /*+ ordered use_nl(f) use_nl(fi) */

       ts.name, fi.file#, f.ktfbfebno,

       f.ktfbfeblks * ts.blocksize, f.ktfbfeblks, f.ktfbfefno

from sys.ts$ ts, sys.x$ktfbfe f, sys.file$ fi

where ts.ts# = f.ktfbfetsn

  and f.ktfbfetsn = fi.ts#

  and f.ktfbfefno = fi.relfile#

  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0

union all

select /*+ ordered use_nl(u) use_nl(fi) */

       ts.name, fi.file#, u.ktfbuebno,

       u.ktfbueblks * ts.blocksize, u.ktfbueblks, u.ktfbuefno

from sys.recyclebin$ rb, sys.ts$ ts, sys.x$ktfbue u, sys.file$ fi

where ts.ts# = rb.ts#

  and rb.ts# = fi.ts#

  and u.ktfbuefno = fi.relfile#

  and u.ktfbuesegtsn = rb.ts#

  and u.ktfbuesegfno = rb.file#

  and u.ktfbuesegbno = rb.block#

  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0

union all

select ts.name, fi.file#, u.block#,

       u.length * ts.blocksize, u.length, u.file#

from sys.ts$ ts, sys.uet$ u, sys.file$ fi, sys.recyclebin$ rb

where ts.ts# = u.ts#

  and u.ts# = fi.ts#

  and u.segfile# = fi.relfile#

  and u.ts# = rb.ts#

  and u.segfile# = rb.file#

  and u.segblock# = rb.block#

  and ts.bitmapped = 0

/

ORACLE 11g中DBA_FREE_SPACE的定义：

create or replace view DBA_FREE_SPACE

    (TABLESPACE_NAME, FILE_ID, BLOCK_ID,

     BYTES, BLOCKS, RELATIVE_FNO)

as

select ts.name, fi.file#, f.block#,

       f.length * ts.blocksize, f.length, f.file#

from sys.ts$ ts, sys.fet$ f, sys.file$ fi

where ts.ts# = f.ts#

  and f.ts# = fi.ts#

  and f.file# = fi.relfile#

  and ts.bitmapped = 0

union all

select /*+ ordered use_nl(f) use_nl(fi) */

       ts.name, fi.file#, f.ktfbfebno,

       f.ktfbfeblks * ts.blocksize, f.ktfbfeblks, f.ktfbfefno

from sys.ts$ ts, sys.x$ktfbfe f, sys.file$ fi

where ts.ts# = f.ktfbfetsn

  and f.ktfbfetsn = fi.ts#

  and f.ktfbfefno = fi.relfile#

  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0

union all

select /*+ ordered use_nl(u) use_nl(fi) */

       ts.name, fi.file#, u.ktfbuebno,

       u.ktfbueblks * ts.blocksize, u.ktfbueblks, u.ktfbuefno

from sys.recyclebin$ rb, sys.ts$ ts, sys.x$ktfbue u, sys.file$ fi

where ts.ts# = rb.ts#

  and rb.ts# = fi.ts#

  and u.ktfbuefno = fi.relfile#

  and u.ktfbuesegtsn = rb.ts#

  and u.ktfbuesegfno = rb.file#

  and u.ktfbuesegbno = rb.block#

  and ts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0

union all

select ts.name, fi.file#, u.block#,

       u.length * ts.blocksize, u.length, u.file#

from sys.ts$ ts, sys.uet$ u, sys.file$ fi, sys.recyclebin$ rb

where ts.ts# = u.ts#

  and u.ts# = fi.ts#

  and u.segfile# = fi.relfile#

  and u.ts# = rb.ts#

  and u.segfile# = rb.file#

  and u.segblock# = rb.block#

  and ts.bitmapped = 0

/

那么在DBA_FREE_SPACE中找到的最大空闲块是否很有可能就是回收站中曾经的一个对象呢？那么我们来测试看看。

SQL> show parameter recyclebin;

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

recyclebin                           string      on

SQL> CREATE TABLE ESCMOWNER.TTT

  2  AS

  3  SELECT * FROM DBA_OBJECTS;

Table created.

SQL> COL OWNER FOR A12;

SQL> COL SEGMENT_NAME FOR A32;

SQL> SELECT OWNER,SEGMENT_NAME, HEADER_FILE, HEADER_BLOCK

  2  FROM DBA_SEGMENTS

  3  WHERE OWNER='ESCMOWNER' AND SEGMENT_NAME='TTT' ;

OWNER        SEGMENT_NAME                     HEADER_FILE HEADER_BLOCK

------------ -------------------------------- ----------- ------------

ESCMOWNER    TTT                                       97       113025

SQL> 

SQL> SELECT * FROM X$KTFBFE WHERE KTFBFEFNO=97;

ADDR                   INDX    INST_ID  KTFBFETSN  KTFBFEFNO  KTFBFEBNO KTFBFEBLKS

---------------- ---------- ---------- ---------- ---------- ---------- ----------

00007F57B2388CA0        222          1          9         97     524169        120

SQL> DROP TABLE ESCMOWNER.TTT;

Table dropped.

SQL> COL ORIGINAL_NAME FOR A16;

SQL> SELECT OBJ#,OWNER#,ORIGINAL_NAME,FILE#,BLOCK# ,FLAGS,SPACE FROM RECYCLEBIN$; 

      OBJ#     OWNER# ORIGINAL_NAME         FILE#     BLOCK#      FLAGS      SPACE

---------- ---------- ---------------- ---------- ---------- ---------- ----------

    805429         73 TTT                      97     113025         30        896

SQL> PURGE DBA_RECYCLEBIN;

DBA Recyclebin purged.

SQL> SELECT * FROM X$KTFBFE WHERE KTFBFEFNO=97 ;

ADDR                   INDX    INST_ID  KTFBFETSN  KTFBFEFNO  KTFBFEBNO KTFBFEBLKS

---------------- ---------- ---------- ---------- ---------- ---------- ----------

00007F57B2388CA0        222          1          9         97     113025          8

00007F57B2388CA0        225          1          9         97     524169        120

SQL> 

如上所示，清空回收站对象后，你会发现X$KTFBFE中多了一条记录，KTFBFEFNO 和 KTFBFEBNO分别为97 ，113025， 这个值显然就是删除对象TTT曾经的FILE_ID（97）和BLOCK_ID（113025）值。

另外，在测试过程中发现，并不是每次的测试结果都是在X$KTFBFE中多一条记录，有时候记录不会变化，但是X$KTFBFE中某条记录的KTFBFEBNO会变化，而这个变化跟清空回收站是有关系的。如下案例所示：

SQL> show parameter recyclebin;

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

recyclebin                           string      on

SQL> CREATE TABLE TEST.TTT

  2  AS

  3  SELECT * FROM DBA_OBJECTS;

Table created.

SQL> COL OWNER FOR A12;

SQL> COL SEGMENT_NAME FOR A32;

SQL> SELECT OWNER,SEGMENT_NAME, HEADER_FILE, HEADER_BLOCK

  2  FROM DBA_SEGMENTS

  3  WHERE OWNER='TEST' AND SEGMENT_NAME='TTT' ;

OWNER        SEGMENT_NAME                     HEADER_FILE HEADER_BLOCK

------------ -------------------------------- ----------- ------------

TEST         TTT                                        5          130

SQL> SELECT * FROM X$KTFBFE WHERE KTFBFEFNO=5 ;

ADDR                   INDX    INST_ID  KTFBFETSN  KTFBFEFNO  KTFBFEBNO KTFBFEBLKS

---------------- ---------- ---------- ---------- ---------- ---------- ----------

00002BA829B19558        150          1          6          5       1280     506752

00002BA829B19558        151          1          6          5     508032      16256

SQL> DROP TABLE TEST.TTT;

Table dropped.

SQL> 

SQL> COL ORIGINAL_NAME FOR A16;

SQL> SELECT OBJ#,OWNER#,ORIGINAL_NAME,FILE#,BLOCK# ,FLAGS,SPACE FROM RECYCLEBIN$; 

      OBJ#     OWNER# ORIGINAL_NAME         FILE#     BLOCK#      FLAGS      SPACE

---------- ---------- ---------------- ---------- ---------- ---------- ----------

     82820         85 TTT                       5        130         30       1152

SQL> SELECT * FROM X$KTFBFE WHERE KTFBFEFNO=5 ;

ADDR                   INDX    INST_ID  KTFBFETSN  KTFBFEFNO  KTFBFEBNO KTFBFEBLKS

---------------- ---------- ---------- ---------- ---------- ---------- ----------

00002BA829B159D8        150          1          6          5       1280     506752

00002BA829B159D8        151          1          6          5     508032      16256

SQL> PURGE DBA_RECYCLEBIN;

DBA Recyclebin purged.

SQL> SELECT * FROM X$KTFBFE WHERE KTFBFEFNO=5 ;

ADDR                   INDX    INST_ID  KTFBFETSN  KTFBFEFNO  KTFBFEBNO KTFBFEBLKS

---------------- ---------- ---------- ---------- ---------- ---------- ----------

00002BA829B159D8        150          1          6          5        128     507904

00002BA829B159D8        151          1          6          5     508032      16256

SQL> 

如上所示，在清空回收站的表以后，你查询X$KTFBFE，就会发现其中一条记录的KTFBFEBNO的变化了，它们的关系为

1280 -1152 = 128

所以，你会看到KTFBFEBNO的值从1280变为了128了。此时你查看DBA_FREE_SPACE，就会看到这样的情况。所以当清空回收站时，有可能是数据库将这个表的空间标记为了空闲块，也有可能是将这个空闲块合并到其它空闲块去了。

X$KTFBFE其实是这几个单词[k]ernel [t]ablespace [f]ile [b]itmapped [f]ree [e]xtents 的首字母。关于这个系统视图最深入的介绍，莫过于这篇文章谈谈Oracle dba_free_space，有兴趣可以验证、测试一下。

 

参考资料：

http://www.cnblogs.com/princessd8251/p/3868487.html

http://dbzone.iteye.com/blog/1020219