The values of the variables, constants, and cursors that a package declares (in either its specification or body) comprise its package state.

If a PL/SQL package declares at least one variable, constant, or cursor, then the package is stateful; otherwise, it is stateless.

Each session that references a package item has its own instantiation of that package. If the package is stateful, the instantiation includes its state.

The package state persists for the life of a session, except in these situations:

• The package is SERIALLY_REUSABLE.

• The package body is recompiled.

  If the body of an instantiated, stateful package is recompiled (either explicitly, with the "ALTER PACKAGE Statement", or implicitly), the next invocation of a subprogram in the package causes Oracle Database to discard the existing package state and raise the exception ORA-04068.

  After PL/SQL raises the exception, a reference to the package causes Oracle Database to re-instantiate the package, which re-initializes it. Therefore, previous changes to the package state are lost.

• Any of the session's instantiated packages are invalidated and revalidated.

  All of a session's package instantiations (including package states) can be lost if any of the session's instantiated packages are invalidated and revalidated.

Oracle Database treats a package as stateless if its state is constant for the life of a session (or longer). This is the case for a package whose items are all compile-time constants.

A compile-time constant is a constant whose value the PL/SQL compiler can determine at compilation time. A constant whose initial value is a literal is always a compile-time constant. A constant whose initial value is not a literal, but which the optimizer reduces to a literal, is also a compile-time constant. Whether the PL/SQL optimizer can reduce a nonliteral expression to a literal depends on optimization level. Therefore, a package that is stateless when compiled at one optimization level might be stateful when compiled at a different optimization level.

Starting with Oracle Database 19c, Release Update 19.23, the initialization parameter SESSION_EXIT_ON_PACKAGE_STATE_ERROR allows you to specify behavior in the event package state is invalidated. When a stateful PL/SQL package undergoes modification, the sessions that have an active instantiation of the package receive the following error when they attempt to run it:

ORA-04068: existing state of package has been discarded

When SESSION_EXIT_ON_PACKAGE_STATE_ERROR is set to TRUE, the session immediately exits instead of just raising ORA-04068. This can be advantageous because many applications are better equipped to handle a session being discarded, simplifying recovery.