disadvantages of oracle

1. It is an incredibly complex engine and usually requires specialized skills to install and maintain.
2. costlier than a comparable MS Sql server database
3. Expert to handle – Every Day maintenance itself require a skilled resource
4. Performance is sub-optimal when data size is large. Performance was lacking in some cases as wait times increased
5. Non-structured Data -- XML, hard to use
6. Many features require additional licensing (either as options or as packs) that increase the total cost
7. Immensely complicated. Of all the databases we use, this one has by far the most moving parts.
8. It is highly recommended to have a dedicated Oracle DBA on staff if you want your databases healthy.
   
9. While the Support Team is incredibly informative, they are often very slow to respond and are often unwilling to answer questions that don't directly solve the problem at hand.
10. From the audit perspective, we have had to customize a lot to meet our electronic work paper needs.
11. The history around the completed task is lacking out of the box.
12. Customer support is sometimes bad and if the ticket is not high priority It could take a lot of time to be attended to.
13. Difficult for beginners to learn
14. Not optimized for low performance systems
15. Function-based indexes are still a problem
16. Query optimization needs improvement.
17. Connection to .NET is kind of complicated and not very easy as compared to Microsoft SQL Server that allows you to connect easier.
18. Patching process can be improved, such as the online process.
19. Error messages that are displayed can be improved.

Reference:

https://www.trustradius.com/products/oracle-database/reviews?f=25&qs=pros-and-cons