默认情况下,SCN多长时间递增一次呢，今天同事突然讨论这个问题，数据库版本如下：

SQL> select * from v$version;

BANNER
--------------------------------------------------------------------------------
Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production
PL/SQL Release 11.2.0.3.0 - Production
CORE    11.2.0.3.0      Production
TNS for Linux: Version 11.2.0.3.0 - Production
NLSRTL Version 11.2.0.3.0 - Production
当前的SCN如下：

SQL> select dbms_flashback.get_system_change_number from dual;

GET_SYSTEM_CHANGE_NUMBER
------------------------
                 1544192

采用scn_to_timestamp获取scn与时间的对应关系如下：

SQL> select scn_to_timestamp(&scn;) from dual;
Enter value for scn: 1544192
old   1: select scn_to_timestamp(&scn;) from dual
new   1: select scn_to_timestamp(1544192) from dual

SCN_TO_TIMESTAMP(1544192)
---------------------------------------------------------------------------
28-mar-12 05.18.36.000000000 pm
将scn递增一次检查时间如下：
SQL> /                           
Enter value for scn: 1544193
old   1: select scn_to_timestamp(&scn;) from dual
new   1: select scn_to_timestamp(1544193) from dual

SCN_TO_TIMESTAMP(1544193)
---------------------------------------------------------------------------

28-MAR-12 05.18.39.000000000 PM

如上可见2个时间差为3秒，

可见时间差仍然没变。

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