问题描述
对于给定的表空间，为什么 dba_extents 中的字节总和不等于 dba_segments 中的字节总和？ （示例脚本后的附加问题。）
sql> with
"SEG" as
( select 'segment_bytes' what,to_char(sum(bytes),'9,999,999') bytes
from dba_segments
where tablespace_name = 'MYDATA'
),"EXT" as
( select 'extent_bytes' what,999') bytes
from dba_extents
where tablespace_name = 'MYDATA'
),"FS" as
( select tablespace_name,sum(bytes) free_bytes
from dba_free_space
where tablespace_name = 'MYDATA'
group by tablespace_name
),"DF" as
( select tablespace_name,sum(bytes) alloc_bytes,sum(user_bytes) user_bytes
from dba_data_files
where tablespace_name = 'MYDATA'
group by tablespace_name
)
select what,bytes from SEG
union all select 'datafile_bytes-freespace' what,to_char(alloc_bytes - nvl(free_bytes,0),999') used_file_bytes
from DF
left join FS
on DF.tablespace_name = FS.tablespace_name
union all select 'datafile_userbytes-freespace' what,to_char(user_bytes - nvl(free_bytes,999') used_user_bytes
from DF
left join FS
on DF.tablespace_name = FS.tablespace_name
union all select what,bytes from EXT
;
WHAT BYTES
---------------------------- ------------------
segment_bytes 2,150,514,819,072
datafile_bytes-freespace 2,528,540,672
datafile_userbytes-freespace 2,412,845,056
extent_bytes 2,056
4 rows selected.
我希望 segment_bytes 等于 extent_bytes 或 datafile_bytes-freespace，但它介于两者之间。
由于段“开销”（跟踪所有范围），segment_bytes 是否大于 extent_bytes？
如果是这样，那么这个段“开销”是否也是数据文件“开销”的一部分？
Oracle 19.1 企业版。提前致谢。
解决方法
例如，dba_segments 和 dba_extents 的区别可能在于 recyclebin 中的对象：请查看我的测试数据库中的结果：
with
seg as (
select segment_name,sum(bytes) b1
from dba_segments
group by segment_name
),ext as (
select segment_name,sum(bytes) b2
from dba_extents
group by segment_name
)
select
seg.segment_name seg1,ext.segment_name seg2,b1,b2
from seg full outer join ext on seg.segment_name=ext.segment_name
where lnnvl(b1=b2)
order by 1,2;
结果：
SEG1 SEG2 B1 B2
------------------------------ ------------------------------ ---------- ----------
BIN$xi7yNJwFcIrgUwIAFaxDaA==$0 65536
BIN$xi7yNJwGcIrgUwIAFaxDaA==$0 65536
_SYSSMU10_2262159254$ _SYSSMU10_2262159254$ 0 4325376
_SYSSMU1_3588498444$ _SYSSMU1_3588498444$ 0 3276800
_SYSSMU2_2971032042$ _SYSSMU2_2971032042$ 0 2228224
_SYSSMU3_3657342154$ _SYSSMU3_3657342154$ 0 2228224
_SYSSMU4_811969446$ _SYSSMU4_811969446$ 0 2293760
_SYSSMU5_3018429039$ _SYSSMU5_3018429039$ 0 3276800
_SYSSMU6_442110264$ _SYSSMU6_442110264$ 0 2228224
_SYSSMU7_2728255665$ _SYSSMU7_2728255665$ 0 2097152
_SYSSMU8_801938064$ _SYSSMU8_801938064$ 0 2228224
_SYSSMU9_647420285$ _SYSSMU9_647420285$ 0 3276800
12 rows selected.
如您所见，前两行是回收站中的对象，因此您可以运行相同的查询并检查您的对象是否也在回收站中。它们在 dba_extents 中不可见，因为它们被 segment_flag:
select text_vc from dba_views where view_name='DBA_EXTENTS';
select ds.owner,ds.segment_name,ds.partition_name,ds.segment_type,ds.tablespace_name,e.ext#,f.file#,e.block#,e.length * ds.blocksize,e.length,e.file#
from sys.uet$ e,sys.sys_dba_segs ds,sys.file$ f
where e.segfile# = ds.relative_fno
and e.segblock# = ds.header_block
and e.ts# = ds.tablespace_id
and e.ts# = f.ts#
and e.file# = f.relfile#
and bitand(NVL(ds.segment_flags,0),1) = 0
and bitand(NVL(ds.segment_flags,65536) = 0
union all
select
ds.owner,e.ktfbueextno,e.ktfbuebno,e.ktfbueblks * ds.blocksize,e.ktfbueblks,e.ktfbuefno
from sys.sys_dba_segs ds,sys.x$ktfbue e,sys.file$ f
where e.ktfbuesegfno = ds.relative_fno
and e.ktfbuesegbno = ds.header_block
and e.ktfbuesegtsn = ds.tablespace_id
and ds.tablespace_id = f.ts#
and e.ktfbuefno = f.relfile#
and bitand(NVL(ds.segment_flags,1) = 1
and bitand(NVL(ds.segment_flags,65536) = 0;
因此，如果我们注释掉那些谓词 (bitand(NVL(segment_flags,0)....) 并检查我们的差异（BIN$... 和 _SYSSMU... 对象），我们会发现哪些谓词将它们过滤掉了：
with
my_dba_extents(
OWNER,SEGMENT_NAME,PARTITION_NAME,SEGMENT_TYPE,TABLESPACE_NAME,EXTENT_ID,FILE_ID,BLOCK_ID,BYTES,BLOCKS,RELATIVE_FNO,segment_flags)
as (
select ds.owner,e.file#,segment_flags
from sys.uet$ e,sys.file$ f
where e.segfile# = ds.relative_fno
and e.segblock# = ds.header_block
and e.ts# = ds.tablespace_id
and e.ts# = f.ts#
and e.file# = f.relfile#
-- and bitand(NVL(ds.segment_flags,1) = 0
-- and bitand(NVL(ds.segment_flags,e.ktfbuefno,segment_flags
from sys.sys_dba_segs ds,sys.file$ f
where e.ktfbuesegfno = ds.relative_fno
and e.ktfbuesegbno = ds.header_block
and e.ktfbuesegtsn = ds.tablespace_id
and ds.tablespace_id = f.ts#
and e.ktfbuefno = f.relfile#
-- and bitand(NVL(ds.segment_flags,1) = 1
-- and bitand(NVL(ds.segment_flags,65536) = 0
)
select
segment_name,bitand(NVL(segment_flags,1) as predicate_1,65536) as predicate_2,case when bitand(NVL(segment_flags,1) = 0 then 'y' else 'n' end pred_1_res,65536) = 0 then 'y' else 'n' end pred_2_res
from my_dba_extents e
where e.segment_name like 'BIN%'
or e.segment_name like '_SYSSMU%';
SEGMENT_NAME PREDICATE_1 PREDICATE_2 PRED_1_RES PRED_2_RES
------------------------------ ----------- ----------- -------------- --------------
_SYSSMU1_3588498444$ 1 0 n y
_SYSSMU1_3588498444$ 1 0 n y
_SYSSMU1_3588498444$ 1 0 n y
_SYSSMU1_3588498444$ 1 0 n y
_SYSSMU1_3588498444$ 1 0 n y
_SYSSMU2_2971032042$ 1 0 n y
_SYSSMU2_2971032042$ 1 0 n y
...
_SYSSMU10_2262159254$ 1 0 n y
_SYSSMU10_2262159254$ 1 0 n y
_SYSSMU10_2262159254$ 1 0 n y
BIN$xi7yNJwGcIrgUwIAFaxDaA==$0 1 65536 n n
BIN$xi7yNJwFcIrgUwIAFaxDaA==$0 1 65536 n n
关于“datafile_bytes-freespace”：不要忘记每个数据文件都有自己的头，所以 dba_segments 和 dba_extents 都不应该算在内。
附注。其他 10 行是撤消段，但这不是您的情况，因为您的查询仅检查您的 MYDATA 表空间，而不是 UNDO。