In the pervious article we have explained the STEPS FOR GRID UGPRADE FROM 12C TO 19C. Now We will explain the steps for downgrade oracle 19c 2 node GRID to oracle 12.1.0.2 GRID.

ENVIRONMENT DETAILS:

2 NODES – dbhost1 and dbhost2
Grid owner – oracle
19C ORACLE_HOME(current) – > /sharearea/crs/grid19c
12C ORACLE_HOME (old) -> /crs/app/oracle/product/grid12c

1. Check the current grid version:( check on both the nodes)

2. Remove the mgmt database:

Currently MGMT is running from dbhost2 i.e node 2 .So run the delete command from NODE 2 only.

NOTE:

So if we try to delete the MGMTDB from node 1, it will throw error as below.

oracle@dbhost1:$ dbca -silent -deleteDatabase -sourceDB -MGMTDB
[FATAL] [DBT-10003] Delete operation for Oracle Grid Infrastructure Management Repository (GIMR) cannot be performed on the current node (dbhost1).
CAUSE: Oracle GIMR is running on a remote node (dbhost2).
ACTION: Invoke DBCA on the remote node (dbhost2) to delete Oracle GIMR.

 

3. Downgrade script execution:

Now we will run the downgrade script first one local node and then on remote node. It need to be run from root user.

Login as root and go to a path where grid owner has write permission. In our case grid owner is oracle.

Downgrade on node 1:(dbhost1) –

login as root and move to a path where oracle has write permission

root$ cd export/home/oracle

/sharearea/crs/grid19c/crs/install/rootcrs.sh -downgrade

Downgrade on node 2( dbhost2)

login as root and move to a path where oracle has write permission

root$ cd /export/home/oracle

/sharearea/crs/grid19c/crs/install/rootcrs.sh -downgrade

4. Remove the 19c grid_home from Active cluster inventory: ( only from one node)

Run this as oracle user from 19C GRID HOME, This need to be run only from one node

cd /sharearea/crs/grid19c/oui/bin

5. Update the active cluster inventory with ORACLE 12C grid home ( only from one node)

Run this as oracle user from 12C GRID HOME, This need to be run only from one node

cd /crs/app/oracle/product/grid12c/oui/bin

6. START THE CRS FROM ORACLE 12C GRID HOME

7. Remove MGMTDB service from cluster.

8.Check crs active version on both nodes:

9.Create the MGMTDB CONTAINER DB:

Here mgmtdb will be created inside +MGMT diskgroup . Make sure +MGMT diskgroup is mounted .

10.Create the MGMTDB PDB:

We have successfully completed the downgrade activity from 19C GRID TO 12.1.0.2 GRID.