set_open_flags

Initializes specific subsystems of the Berkeley DB environment.

The syntax of the entry in the DB_CONFIG is a single line with the string set_open_flags, one or more whitespace characters, the method flag parameter as a string, optionally one or more whitespace characters, and the string on or off. If the optional string is omitted, the default is on; for example, set_open_flags DB_INIT_REP or set_open_flags DB_INIT_REP on. Because the DB_CONFIG file is read when the database environment is opened, it will silently overrule configuration done before that time.

The method flag parameters are as follows:

• DB_INIT_REP

  Enables/disables DB_INIT_REP in the DB_ENV->open method. For example:

  set_open_flags DB_INIT_REP on

  This enables initializing the replication subsystem. This subsystem should be used whenever an application plans on using replication. This setting overwrites the DB_INIT_REP flag passed from the application's DB_ENV->open method.

• DB_PRIVATE

  Enables/disables DB_PRIVATE in the DB_ENV->open method. For example:

  set_open_flags DB_PRIVATE on

  This enables region memory allocation from the heap instead of from memory backed by the filesystem or system shared memory. This flag implies the environment will only be accessed by a single process (although that process may be multithreaded). This flag has two effects on the Berkeley DB environment. First, all underlying data structures are allocated from per-process memory instead of from shared memory that is accessible to more than a single process. Second, mutexes are only configured to work between threads. This setting overwrites the DB_PRIVATE flag passed from the application's DB_ENV->open method.

• DB_THREAD

  Enables/disables DB_THREAD in the DB_ENV->open method. For example:

  set_open_flags DB_THREAD on

  This enables the DB_ENV handle returned by the DB_ENV->open method to be free-threaded; that is, concurrently usable by multiple threads in the address space. This setting overwrites the DB_THREAD flag passed from the application's DB_ENV->open method.