1、查询表空间时间长
在查询表空间剩余空间时，常遇到执行时间过长，因为有一个DBA_FREE_SPACE 空闲空间需要统计回收站recyclebin$的信息，如下：
查看catspace.sql脚本，有一段DBA_FREE_SPACE的脚本：
[oracle@oracle11g admin]$ more $ORACLE_HOME/rdbms/admin/catspace.sql
create or replace view DBA_FREE_SPACE
(TABLESPACE_NAME, FILE_ID, BLOCK_ID,
BYTES, BLOCKS, RELATIVE_FNO)
as
select ts.name, fi.file#, f.block#,
f.length * ts.blocksize, f.length, f.file#
from sys.ts$ ts, sys.fet$ f, sys.file$ fi
where ts.ts# = f.ts#
andf.ts# = fi.ts#
andf.file# = fi.relfile#
andts.bitmapped = 0
union all
select
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
andf.ktfbfetsn = fi.ts#
andf.ktfbfefno = fi.relfile#
andts.bitmapped <> 0 and ts.online$ in (1,4) and ts.contents$ = 0
union all
select
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#
andrb.ts# = fi.ts#
andu.ktfbuefno = fi.relfile#
andu.ktfbuesegtsn = rb.ts#
andu.ktfbuesegfno = rb.file#
andu.ktfbuesegbno = rb.block#
andts.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$rb
where ts.ts# = u.ts#
andu.ts# = fi.ts#
andu.segfile# = fi.relfile#
andu.ts# = rb.ts#
andu.segfile# = rb.file#
andu.segblock# = rb.block#
andts.bitmapped = 0
2、查看回收站 dba_recyclebin 信息
SQL> select count(1) from recyclebin$; 同dba_recyclebin系统表
COUNT(1)
----------
60035
3、加快查询表空间
如果不需要闪回，恢复(有备份除外)等操作(谨慎)，可以选择清空回收站，使得查询表空间加快。
SQL> purge dba_recyclebin;
DBA Recyclebin purged.