關於oracle db 11gR2版本上的_external_scn_rejection_threshold_hours參數和scn headroom補丁問題，11gr2headroom

關於oracle db 11gR2版本上的_external_scn_rejection_threshold_hours參數和scn headroom補丁問題，11gr2headroom
關於oracle db 11gR2版本上的_external_scn_rejection_threshold_hours參數和scn headroom補丁問題

來自於：
Installing, Executing and Interpreting output from the "scnhealthcheck.sql" script (文檔 ID 1393363.1)

第一點：

In addition to the above result the script output may advise to set the hidden parameter "_external_scn_rejection_threshold_hours" on some Oracle versions. The following text gives more information about setting this parameter:

Set _external_scn_rejection_threshold_hours=24 after apply
Oracle recommends setting this parameter to the value 24 in 10g and 11.1 releases - it does not need to be set in 11.2 or later releases. The parameter is static and so must be set in the init.ora or spfile used to start the instance. 
eg:
In init.ora: 
  # Set threshold on dd/mon/yyyy - See MOS Document 1393363.1
  _external_scn_rejection_threshold_hours = 24 
 
In the spfile: 
  alter system set "_external_scn_rejection_threshold_hours" = 24 
   comment='Set threshold on dd/mon/yyyy - See MOS Document 1393363.1' 
   scope=spfile ;

從以上可以看出，在 11.2及其更高的版本上，是無需設定_external_scn_rejection_threshold_hours參數的。

第二點：

Please note that there are no SCN hardening fixes for the following versions. The recommendation for these versions is to upgrade to a newer release:  All versions up to and including 9.2.0.7  Versions 10.1.0.2 to 10.1.0.4 inclusive  Versions 10.2.0.1 and 10.2.0.2  Version 11.1.0.6  Version 11.2.0.1

從這句話可以看出：以上版本的oracle資料庫軟體沒有修複scn headroom 的補丁。請升級到更新的版本。這一招夠狠的。

Versions 11.2.0.4 and 12.1.0.1 onwards already include the main SCN fixes but the "scnhealthcheck" script described above can still be used on those releases to check the current headroom.

從這句話可以看出，在11.2.0.4及其12.1.0.1版本上，已經包括了對scn問題的修複（fixes）,說白了，11.2.0.4及其12.1.0.1的程式版本已經修複了scn headroom問題。
對於Oracle的資料泵知識中FLASHBACK_SCN屬性中提到的SCN時刻的問題

這玩意解釋起來比較複雜。給你一下網址學習一下吧，講的很詳細。

blog.csdn.net/...438016
 
ORACLE查詢SCN號有點小問題 望解納

這麼查

col current_scn for 99999999999
select current_scn from v$database;

CURRENT_SCN
------------
4774525