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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

程序员文章站 2022-09-06 15:09:47
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...

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
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。

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$)中的空间计算为*空间,加入到dba_free_space字典中。在$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> 
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:

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> 
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