Ora-19706:invalid SCN

Today Live Dblink reported Ora-19706:invalid SCN, the database version is 11.2.0.4. Check the next Metalink, the general meaning is through the Dblink access, two databases will do the SCN number synchronization, SCN headroom results must be more than the parameters _external_scn_rejection_threshold_ The value of the hours is large.

installing, executing and interpreting output from the "Scnhealthcheck.sql" script (document ID 1393363.1)

applies To:
Oracle database-enterprise edition-version 10.1.0.5 to 12.1.0.1 [Release 10.1 to 12.1]
Oracle Database-standard edition-version 10.1.0.5 to 12.1.0.1 [Release 10.1 to 12.1]
Information in this document applies to any platform.
PURPOSE
This document describes the ' scnhealthcheck.sql ' script, including where to download the script, how to execute it and how To interpret the output.
For customers with Enterprise Manager a alternative to this script was to obtain and use the patch described in document:1 404410.1. The "Recommended Actions" section of that document would direct you back to this document for details of what act Ion to take.
SCOPE
This document was intended for Oracle DBAs.
The "scnhealthcheck.sql" script described here's intended for execution on any database version 10.1 or higher, except ph ysical standby databases. For physical standby databases The script should is executed against the primary.
DETAILS
Installing the "scnhealthcheck.sql" script
The "scnhealthcheck.sql" script can be downloaded here:patch:13498243.
If you install the patch then it'll create "Scnhealthcheck.sql" in the $ORACLE _home/rdbms/admin directory.
Alternatively you can use the script directly from the unzipped patch without actually installing it in your $ORACLE _home.
Executing "scnhealthcheck.sql"
"Scnhealthcheck.sql" can is executed as any DBA user of a database. It can be used in any 10.1 or higher database, regardless the patch level.
To execute the script:
Change to the directory where the ' scnhealthcheck.sql ' script is located.
Use Sqlplus to execute the script spooling output to a file.
Eg:use an appropriate spool path for your platform below.
Sqlplus system/xxxxx
Spool/tmp/scncheck_out
@scnhealthcheck
Spool off
Exit
Interpreting "Scnhealthcheck.sql" Output
The output gives a snapshot of the SCN health at a given point in time. Example output might look like this:
------------------------------------------------------------
Scnhealthcheck
------------------------------------------------------------
Current DATE:2012/01/17 01:01:09
Current scn:384089
version:11.1.0.7.0
------------------------------------------------------------
Result:a-SCN Headroom is good
Apply the latest recommended patches
Based on your maintenance schedule
and set _external_scn_rejection_threshold_hours=24 after apply.
For further information review MOS document ID 1393363.1
------------------------------------------------------------
Take the appropriate action as indicated by the "Result":
result:a-SCN headroom is good
SCN Health is good on this time. The majority of databases is expected to fall in this category. You were recommended to ensure that your database was patched to the current level as indicated by ' My Oracle support ' recom Mendations using your normal maintenance schedule. No additional action is required on this time. See note #1 and #2 in the Notes section below.
result:b-SCN headroom is low
SCN Health is low. You were recommended to ensure that your database was patched to the current level as indicated by ' My Oracle support ' recom Mendations immediately rather than waiting for your normal maintenance window. Once patched The headroom is expected to increase over time. Continue to monitor the health daily. Please note that it could take several days or weeks after patching for the output of the headroom is good. See note #1 and #3 in the Notes section below.
result:c-SCN headroom is low
SCN Health is low. This database appears to has a high rate of SCN increase. You were recommended to ensure that your database was patched to the current level as indicated by ' My Oracle support ' recom Mendations immediately. If you had not already do so, follow the instructions in document:1388639.1 to log a Service Request with Oracle Support So, additional advice can be given. See note #1 and #3 in the Notes section below.
In addition to the above result the script output could advise to set the hidden parameter "_external_scn_rejection_threshol D_hours "on some Oracle versions. The following text gives more information on setting this parameter:
Set _external_scn_rejection_threshold_hours=24 after apply
The hidden parameter "_external_scn_rejection_threshold_hours" is introduced in January Critical Patch Update (CPU) A nd Patch Set Update (PSU) releases (and related bundles). Oracle recommends setting this parameter to the value of 10g and 11.1 releases-it does not need to is set in 11.2 or Later releases. The parameter is a static and so must being 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;
Why does I need to set "_external_scn_rejection_threshold_hours" = 24?
Oracle has many hidden parameters which all with default or derived values, and those parameters is not generally intende D to is set by customers. Oracle determined, the most suitable value of this new hidden parameter is "" "and", "This value should be used AC Ross all releases. 10g and 11.1 January CPU/PSU releases a different default value compiled in and so this setting had to be made Explicitly on those releases to ensure, the required value of is used. Customers is not expected to tune this value themselves. Latest releases should has a default value of "" "already.
Notes:
#1 for help with the current recommendations see:
document:756671.1 for Latest Recommended Database patches.
document:331.1 Item "2. Plan for general information on how to find recommended patches
document:1374524.1 for January patch Set update and Critical patch update availability. This documents the absolute minimum patch level for each release-you is strongly advised to use the current Recommendat Ions in preference to these minimum levels, and in particular use CPU/PSU from July-or later where available (see D ocument:1455387.1 for July cpu/psu availability).
document:742060.1 Release Schedule and patching End Dates of current Database releases
Please note that there is no SCN hardening fixes for the following versions. The recommendation for these versions are to upgrade to a newer release:
All versions 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
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 is used on those releases to check the current headroom.

#2 the output of the "Scnhealthcheck" script is a snapshot for the current point in time. As database activity can vary the output may is different at a later time. If any execution of the SQL shows output and than "Result:a" then please follow the guidance above.

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#3 after applying patches it could take some time (days or weeks) before the headroom grows sufficient Ly for the script "Result:a".

To confirm this headroom is increasing you can change the ' verbose=false ' clause in ' scnhealthcheck.sql ' to ' verbose=t RUE. " This would cause the script to output a additional "SCN headroom" line. After patching one should see the "SCN headroom" value increase slowly over time. Note that the value cannot increase is more than 1.0 per day. If the value continues to decrease, or becomes a increasingly large negative number, then if you had not already do so Follow the instructions in document:1388639.1 to log a Service Request with Oracle support.

Ora-19706:invalid SCN