what happens in cutover phase of adop in R12.2

Cutover phase of adop   is downtime phase of Online patching cycle. We should ensure no user access is there in that period as application processes are restarted.
Before running the cutover command, ensure you are ready to commit to application of the selected patches. Once cutover is complete, it is not possible to revert to the previous edition

Cutover phase  of adop has following steps

(1) Shut down internal concurrent manager: The adop utility signals the internal concurrent manager to shut down, but will wait for any existing concurrent requests to finish before it proceeds with cutover actions. The system is still available to users during this waiting period.
If you do not wish to wait indefinitely for concurrent requests to finish, specify the option cm_wait=<maximum_minutes_to_wait> with a number of minutes that reflects your operational needs
On production systems, do not specify cm_wait, but monitor progress of concurrent tasks and take manual action on them if needed.It is good to schedule cutover during the time where least jobs are running.
On non-production systems, we specify cm_wait to limit the waiting time before cutover proceeds as it is development and we can tolerate abort of Concurrent Manager
Note: Cutover will take longer if it has to wait for long-running concurrent processes to complete. In such a case, you can expect to see an informational message of the form:
[STATEMENT] [END ] Waiting for ICM to go down
If you do not want to wait for in-progress concurrent requests to finish normally, you can terminate the internal concurrent manager by executing the adcmctl.sh abort command from a different shell
This task is performed by $FND_TOP/bin/txkADOPCutOverPhaseCtrlScript.pl script

(2) Shut down application tier services: All application tier services are brought down. During this period, the system is unavailable to users.
This task is performed by $FND_TOP/bin/txkADOPCutOverPhaseCtrlScript.pl script

(3) Cutover database: Promote patch database edition to become the new run database edition, using adzdpmgr.pl script.
This task is performed by $FND_TOP/bin/txkADOPCutOverPhaseCtrlScript.pl script

(4) Cutover file system: Promote patch file system to become the new run file system, switching the $FILE_EDITION values in the patch and run enviroments. The current patch APPL_TOP becomes the new run APPL_TOP, and the current run APPL_TOP becomes the new patch APPL_TOP.
This task is completed by Autoconfig

(5) Terminate old database sessions: Terminate any database connections to the old run edition of the database.
This task is performed by $FND_TOP/bin/txkADOPCutOverPhaseCtrlScript.pl script

(6) Start application tier services: Application tier services are restarted, on the new run edition. The system is now available again to users.
This task is performed by $FND_TOP/bin/txkADOPCutOverPhaseCtrlScript.pl script

Example .
$ adop phase=cutover
This will promote the patch edition to be the new run edition, as well as switching the patch and run labels on the file systems (and thereby, as noted above, changing the patch file system to be the new run file system and the run file system to be the new patch file system).

Deferring Application Tier Restart at Cutover

Many times you may need to perform additional manual steps after cutover but before restarting the application tier services. If this is the case, you can supply an additional parameter to the cutover command that causes the application services to remain shut down:
$ adop phase=cutover mtrestart=no
With this parameter, cutover will complete without restarting the application tier services. You can perform any additional steps that require the services to be shut down, and then start the application tier services manually using the adstrtal.sh script.

JAR Files and Cutover

In an online patching cycle, the requisite JAR files are initially stored in the $APPL_TOP/admin/<SID>/out directory, and then uploaded into the database during the cutover phase. Therefore, the out directory must not be deleted at least until cutover is complete.

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