Berkeley DB Reference Guide: Upgrading Berkeley DB Applications

Release 4.4: DB_JOINENV

The semantics of joining existing Berkeley DB database environments has changed in the 4.4 release. Previously:

1. Applications joining existing environments, but not configuring some of the subsystems configured in the environment when it was created, would not be configured for those subsystems.

2. Applications joining existing environments, but configuring additional subsystems in addition to the subsystems configured in the environment when it was created, would cause additional subsystems to be configured in the database environment.

In the 4.4 release, the semantics have been simplified to make it easier to write robust applications. In the 4.4 release:

1. Applications joining existing environments, but not configuring some of the subsystems configured in the environment when it was created, will now automatically be configured for all of the subsystems configured in the environment.

2. Applications joining existing environments, but configuring additional subsystems in addition to the subsystems configured in the environment when it was created, will fail, as no additional subsystems can be configured for a database environment after it is created.

In other words, the choice of subsystems initialized for a Berkeley DB database environment is specified by the thread of control initially creating the environment. Any subsequent thread of control joining the environment will automatically be configured to use the same subsystems as were created in the environment (unless the thread of control requests a subsystem not available in the environment, which will fail). Applications joining an environment, able to adapt to whatever subsystems have been configured in the environment, should open the environment without specifying any subsystem flags. Applications joining an environment, requiring specific subsystems from their environments, should open the environment specifying those specific subsystem flags.

The DB_JOINENV flag has been changed to have no effect in the Berkeley DB 4.4 release. Applications should require no changes, although uses of the DB_JOINENV flag may be removed.

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