Run Apex 4.2.6 and APEX 5 on same database parallel

Question

Hi,
Is it possible to install Apex 4.2.6 and Apex 5.0 on the same database? If Apex Listener is used as Application Server, do I have to install two different Listener Instances as well?
Thanks

Answer 1

Hi,
I do understand your argument that there should be no custom code in SYS. But in the case of the APEX engine it's a must have to guarantee security. You might know or not know, but APEX is using SYS.DBMS_SQL_SYS package (a more powerful version of the DBMS_SQL package) to execute application code/DML statements with the privileges of the parsing schema of the executed application. Obviously you don't want to grant execute to that package to another schema than SYS because of the power of package to run code in the name of another schema/user.
Do not have an issue with public synonyms though - understandable from a scope resolution perspective. For multiple versions though, scope should be able to be dealt with using the Oracle logon schema (as configured on web server side) and private synonyms?
Unfortunately this would not be sufficient because the Oracle Logon Schema (most of the time called APEX_PUBLIC_USER) specified for mod_plsql/ORDS is only used to call the entry points of the APEX Engine like the F procedure or WWV_FLOW.SHOW and WWV_FLOW.ACCEPT. This would work fine until custom PL/SQL code or SQL/DML statements of your application have to be executed. This is not done with the privileges / scope of APEX_PUBLIC_USER, instead the code will be executed with the Parsing Schema specified for your application (that's where the above described SYS package comes into play). Otherwise APEX_PUBLIC_USER would have to be a super highly privileged user with access to any schema, which isn't the case. Instead it's a super low privileged user.
Let's continue our example. If the application PL/SQL code / SQL or DML statement references one of our public APIs like V, APEX_APPLICATION, APEX_UTIL, ... or an APEX view we are in the the situation that the application schema has to resolve those references. But a schema can just point to one APEX version.
How could that be solved?
When copying the application to the new APEX version, the application parsing schema would have to be changed to a new 'proxy' application schema with access to the original application schema. The 'proxy' schema would point it's private synonyms to the new APEX version. But even then it's getting tricky if the original application schema has definer rights packages which do reference APEX apis, because those would still point to the public synonyms. As I said, it's not so easy and there are many traps customers could fall into ending up with a situation where it's hard to diagnose if an application is trying to call different versions of APEX in the same runtime session.
But as I said, we are totally aware of the situation that customers would like to do a slower one by one application upgrade of their APEX installations to avoid breaking apps.
Regards
Patrick
Member of the APEX development team
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