Any impact on existing SQL, PL/SQL scripts and data model due to Oracle DB upgrade from 12cto 19c?

Question

I wanted to discuss my understanding for impact on existing SQL, PL/SQL scripts and data model due to DB upgrade from 12cto 19c: As per my own research and understanding-

1. There is no identified change which may lead to failure of my existing SQL and PL/SQL during ETL load and reporting queries.
2. There is no identified data type change which may impact existing data model. Only extended data type feature is DE supported in Oracle
   Database 19c.We are not using extended data type in existing data model.
3. The database layout of key features between 12.2 and 19c has not been
   changed. Hence, your setup for 12.2 and 19c should not result into any issue

Please let me know any further comment or input.

Answer 1

In theory you may not have any incompatilbity or issue. But experience show that there always some risks involved in upgrading an Oracle database: mainly changes in SQL execution plans because the Cost Based Optimizer (CBO) is always improved: generally it's OK but you might have some exception (ie an execution plan that has changed and become slow); this is why performance testing should be a mandatory step in your upgrade test. Never do an upgrade directly in production without testing it on a physical copy of the database: doing so would be a possible recipe for disaster !

In addition to Oracle documentation and support.oracle.com, I suggest to always check Mike Dietrich blog which is one of the best - if not the best - Oracle upgrade knowledge base: https://mikedietrichde.com/

If there were no issues during Oracle upgrade and patching, Mike Dietrich blog would be very different from what it is ...