Oracle, Users as Instances

Question

A client has been referring me to their different Oracle "databases". After a data migration mix-up, it occurred to me that these various databases are all the same database. They've just broken up the same instance with multiple users and strict permissions.

So, user1 has a CUSTOMER table, user1.CUSTOMER and user2 has a CUSTOMER table user2.CUSTOMER.
The data in those tables is completely separate, and managed by different instances of an application.

I've never seen this done before; Is this a standard, acceptable practice?

Is there a specific performance and maintenance scheme for this type of setup? Or, is this the wild west?

thanks

Answer 1

This is a normal standard practice in Oracle environments. Oracle environments are one big application with one or few schemas, or a multitude of small applications grown over time.

Of course there are a number of architectural design decisions to make. For instance, when placing multiple applications in one database, the applications may influence each others. Over time, Oracle has been enhancing the technology stack to restrict the influence applications can have on each other. For instance, you can nowadays distribute the resources differently per user. But for instance an application running wild can flush the whole cache, impacting other applications. Starting with Oracle 12c, Oracle Corp. has even further improved the isolation by creating a structure that more resembles the Microsoft SQL Server approach with separate "databases", but 12c even extends that further. For instance because an Oracle container database can still contain multiple databases and it's own data dictionary (enterprise edition only allows more than 1 container database).

In general, I do not recommend putting many serious/large applications in one Oracle database. For instance, when you upgrade one of them, you need to make sure that all other applications are compatible with a possible new minor release of Oracle needed. So when you merge multiple applications in one database, make sure that you can control that they are all certified at the same time for the same Oracle version. For instance because it are inhouse packages.