Zero Downtime Migration – Physical Online Migration and Testing

Testing is an essential part of any migration project. With ZDM and the Physical Online method it has become a lot easier. Before going live (i.e. doing the Data Guard switchover) you can test on your production data on your future production system – the OCI database. That’s cool.

Concept

For the duration of your test convert the OCI target database into a snapshot standby database. A short recap on snapshot standby database:

  • A snapshot standby database is a type of updatable standby database that provides full data protection for a primary database.
  • A snapshot standby database receives and archives, but does not apply, redo data from its primary database. Redo data received from the primary database is applied when a snapshot standby database is converted back into a physical standby database, after discarding all local updates to the snapshot standby database.
  • A snapshot standby database diverges from its primary database over time because redo data from the primary database is not applied as it is received. Local updates to the snapshot standby database cause additional divergence. The data in the primary database is fully protected however, because a snapshot standby can be converted back into a physical standby database at any time, and the redo data received from the primary is then applied.

The plan is:

  1. Build the standby database in OCI.
  2. Migration is currently paused at ZDM_CONFIGURE_DG_SRC (-pauseafter ZDM_CONFIGURE_DG_SRC).
  3. Convert the OCI target database – which is a physical standby – into a snapshot standby.
  4. Do your test. Do whatever you want. The database is protected by Flashback Database, so you can insert and delete data, truncate, add tablespaces, you name it.
  5. When you are done with your tests, convert the OCI target database back into a physical standby database. Implicitly, the database is flashed back, and now the redo is getting applied again.
  6. After a little while the target database is now back in sync again.
  7. Complete migration at your will.

How

To convert the standby database to a snapshot standby database using broker (CDB19_fra3zt is the target DB_UNIQUE_NAME):

convert database 'CDB19_fra3zt' to snapshot standby;

Or manually:

alter database recover managed standby database cancel;
shutdown immediate
startup mount
alter database convert to snapshot standby;
alter database open;

Now, the database is opened in READ WRITE mode and you can use it for testing. To convert back to a physical standby database:

convert database 'CDB19_fra3zt' to physical standby;

Or manually:

shutdown immediate
startup mount
alter database convert to physical standby;
shutdown immediate
startup
alter database recover managed standby database disconnect from session;

You can even do this multiple times if you want several test runs on your OCI database.

Conclusion

One of the really cool features of ZDM is that you can use my standby database for testing in OCI – before I decide to do the switchover. You can achieve this by converting to a snapshot standby database.