Review these scenarios to determine if you must relink your applications after upgrading.

If your client and server are on different computers, or are in different Oracle home directories on the same computer, and you upgrade the Oracle Database server software without changing the client software, then you are not required to precompile, compile, or relink your applications.

In this set of scenarios, client software using Oracle Databases are in separate locations from the server software, and the client software continues to function without direct effects from the upgrade.

However, if your applications are using the same Oracle home as the Oracle Database server, then your server upgrade also upgrades your client software, and you must follow the rules for upgrading Oracle Database client software.

If you run a precompiler or OCI application against a database server, then Oracle recommends that the release of the database server software is equal to or later than the client software release.

This recommendation configuration is not strictly required.

For example: If your client software is Oracle 12c release 2 (12.2.0.1), then if you run precompiler applications on the client against, the server, Oracle recommends that your server software is Oracle 12c release 2 (12.2) or later.

You can link the code generated by precompiler applications and Oracle Call Interface (OCI) with a release of the client library that equals or is later than the server release.

The OCI runtime library that you use must either be the same release, or a later release, than the release of the OCI library with which the application was developed.

Statically-linked code can be incompatible with error messages in the upgraded ORACLE_HOME.

You must relink statically-linked OCI applications for both major and minor releases. The statically-linked Oracle client-side library code may be incompatible with the error messages in the upgraded ORACLE_HOME. For example, if an error message is updated with additional parameters, then it becomes incompatible with the statically-linked code.

Dynamically linked OCI applications from Oracle Database 10g Release 1 (10.1) and later releases are upward-compatible with the current release.

The Oracle client-side dynamic library is upward-compatible with the previous version of the library. Oracle Universal Installer creates a symbolic link for the previous version of the library that resolves to the current version. Therefore, an application that is dynamically linked with the previous version of the Oracle client-side dynamic library does not require relinking to operate with the current version of the Oracle client-side library.