About the _ external_scn_rejection_threshold_hours parameter and scn headroom patch in oracle db 11gR2, 11gr2headroom

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About the _ external_scn_rejection_threshold_hours parameter and scn headroom patch in oracle db 11gR2, 11gr2headroom
About the _ external_scn_rejection_threshold_hours parameter and scn headroom patch in oracle db 11gR2

From:
Installing, Executing and Interpreting output from the "scnhealthcheck. SQL" script (Document ID 1393363.1)

First:

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;

From the above, we can see that in version 11.2 and later, the _ external_scn_rejection_threshold_hours parameter does not need to be set.

Second point:

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
From this sentence, we can see that the above version of oracle Database software does not fix the scn headroom patch. Upgrade to the latest version. This is a tough trick.

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.
From this sentence, we can see that in 11.2.0.4 and 12.1.0.1, the fixed scn problem (fixes) has been included. To put it bluntly, the program version of 11.2.0.4 and 12.1.0.1 has fixed the scn headroom problem.
The SCN moment mentioned in the FLASHBACK_SCN attribute in Oracle Data Pump knowledge

This is complicated to explain. Let's take a look at the website. It's very detailed.

Blog.csdn.net/..438016

There is a small problem in querying the SCN number in ORACLE.

So query

Col current_scn for 99999999999
Select current_scn from v $ database;

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

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