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;">
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）
下面通过一个例子来演示一下，详情如下所示
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,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$BH
10 WHERE FILE# = 4
11 AND BLOCK# = 266;
OBJD FILE# BLOCK# CLASS# TS# CACHEHINT STATUS D
---------- ---------- ---------- ---------- ---------- ---------- ---------- -
76090 4 266 4 4 15 cr N
76090 4 266 4 4 15 cr N
76090 4 266 4 4 15 cr N
sql> SELECT OWNER,OBJECT_NAME FROM DBA_OBJECTS WHERE OBJECT_ID=76090;
OWNER OBJECT_NAME
------------ ------------------------------------------------------------
TEST EMPLOYEE
clip_image001
昨天在群里讨论一个关于空闲块的问题时，我验证测试时，发现一个奇怪的现象，使用下面sql找到了一个最大空闲块。
sql;">
SELECT UPPER(F.TABLESPACE_NAME) AS "表空间名",D.TOT_GROOTTE_MB AS "表空间大小(M)",D.TOT_GROOTTE_MB - F.TOTAL_BYTES AS "已使用空间(M)",TO_CHAR(ROUND((D.TOT_GROOTTE_MB - F.TOTAL_BYTES) / D.TOT_GROOTTE_MB * 100,2),'990.99')
AS "使用比",F.TOTAL_BYTES AS "空闲空间(M)",F.MAX_BYTES AS "最大空闲块(M)"
FROM
(SELECT TABLESPACE_NAME,ROUND(SUM(BYTES) / (1024 * 1024),2) TOTAL_BYTES,ROUND(MAX(BYTES) / (1024 * 1024),2) MAX_BYTES
FROM SYS.DBA_FREE_SPACE
GROUP BY TABLESPACE_NAME
) F,(SELECT DD.TABLESPACE_NAME,ROUND(SUM(DD.BYTES) / (1024 * 1024),2) TOT_GROOTTE_MB
FROM SYS.DBA_DATA_FILES DD
GROUP BY DD.TABLESPACE_NAME
) D
WHERE D.TABLESPACE_NAME = F.TABLESPACE_NAME;
SELECT FILE_ID,BLOCK_ID,BYTES,BLOCKS
FROM DBA_FREE_SPACE
WHERE TABLESPACE_NAME=&TABLESPACE_NAME
ORDER BY BYTES DESC;
然后我发现使用上面两个sql查不到对应的对象。如下截图所示：
后面查了一下资料，发现在Oracle Database 10g引入了回收站功能后，会将回收站（RECYCLEBIN$）中的空间计算为自由空间，加入到dba_free_space字典中。在$ORACLE_HOME/rdbms/admin/catspace.sql中，你可以找到视图DBA_FREE_SPACE的定义，脚本如下：
ORACLE 10g中DBA_FREE_SPACE的定义：
sql;">
create or replace view DBA_FREE_SPACE
(TABLESPACE_NAME,FILE_ID,BLOCKS,RELATIVE_FNO)
as
select ts.name,fi.file#,f.block#,f.length * ts.blocksize,f.length,f.file#
from sys.ts$ 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,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,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,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,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。
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,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$KTFBFE WHERE KTFBFEFNO=97;
ADDR INDX INST_ID KTFBFETSN KTFBFEFNO KTFBFEBNO KTFBFEBLKS
---------------- ---------- ---------- ---------- ---------- ---------- ----------
00007F57B2388CA0 222 1 9 97 524169 120
sql> DROP TABLE ESCMOWNER.TTT;
Table dropped.
sql> COL ORIGINAL_NAME FOR A16;
sql> SELECT OBJ#,OWNER#,ORIGINAL_NAME,FLAGS,SPACE FROM RECYCLEBIN$;
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$KTFBFE WHERE KTFBFEFNO=97 ;
ADDR INDX INST_ID KTFBFETSN KTFBFEFNO KTFBFEBNO KTFBFEBLKS
---------------- ---------- ---------- ---------- ---------- ---------- ----------
00007F57B2388CA0 222 1 9 97 113025 8
00007F57B2388CA0 225 1 9 97 524169 120
sql>
clip_image003
如上所示，清空回收站对象后，你会发现X$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：
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,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$KTFBFE WHERE KTFBFEFNO=5 ;
ADDR INDX INST_ID KTFBFETSN KTFBFEFNO KTFBFEBNO KTFBFEBLKS
---------------- ---------- ---------- ---------- ---------- ---------- ----------
00002BA829B19558 150 1 6 5 1280 506752
00002BA829B19558 151 1 6 5 508032 16256
sql> DROP TABLE TEST.TTT;
Table dropped.
sql>
sql> COL ORIGINAL_NAME FOR A16;
sql> SELECT OBJ#,SPACE FROM RECYCLEBIN$;
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>
clip_image004
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。
以上所述是小编给大家介绍的关于ORACLE通过file_id与block_id定位数据库对象遇到的问题引发的思考，希望对大家有所帮助，如果大家有任何疑问欢迎给我留言，小编会及时回复大家的！
原文链接：https://www.f2er.com/oracle/64926.html