绝对文件号的意义在什么地方

etl2007

根据前贴
http://t.askmaclean.com/thread-701-1-1.html

要确认一个表中一条记录在哪个数据文件中
只需要知道表空间名称和相对文件号就可得到结果
数据读取数据的时候应当也是按照这个逻辑

那么绝对文件号看起来就没有什么实际的意义了？
我这样理解对吗？

Maclean Liu(刘相兵

Oracle Database assigns each datafile two associated file numbers, an absolute file number and a relative file number, that are used to uniquely identify it. These numbers are described in the following table:
Type of File Number         Description


Absolute         Uniquely identifies a datafile in the database. This file number can be used in many SQL statements that reference datafiles in place of using the file name. The absolute file number can be found in the FILE# column of the V$DATAFILE or V$TEMPFILE view, or in the FILE_ID column of the DBA_DATA_FILES or DBA_TEMP_FILES view.


Relative         Uniquely identifies a datafile within a tablespace. For small and medium size databases, relative file numbers usually have the same value as the absolute file number. However, when the number of datafiles in a database exceeds a threshold (typically 1023), the relative file number differs from the absolute file number. In a bigfile tablespace, the relative file number is always 1024 (4096 on OS/390 platform).



http://docs.oracle.com/cd/E14072 ... 10595/dfiles001.htm


Absolute File Number is unique across Database where as Relative file number is unique within tablespace but not across database.

There is a limit of 1023 datafiles in a tablespace thus 1023 relative file numbers in a tablespace.