#include <db.h>

DB_ENV->close(DB_ENV *dbenv, u_int32_t flags);  

The DB_ENV->close() method closes the Berkeley DB environment, freeing any allocated resources and closing all database handles opened with this environment handle, as well as closing any underlying subsystems.

When you call the DB_ENV->close() method, all open DB handles and DBcursor handles are closed automatically by this function. And, when you close a database handle, all cursors opened with it are closed automatically.

In multiple threads of control, each thread of control opens a database environment and the database handles within it. When you close each database handle using the DB_ENV->close() method, by default, the database is not synchronized and is similar to calling the DB->close(DB_NOSYNC) method. This is to avoid unncessary database synchronization when there are multiple environment handles open. To ensure all open database handles are synchronized when you close the last environment handle, set the flag parameter value of the DB_ENV->close() method to DB_FORCESYNC. This is similar to calling the DB->close(0) method to close each database handle.

If a database close operation fails, the method returns a non-zero error value for the first instance of such an error, and continues to close the rest of the database and environment handles.

The DB_ENV handle should not be closed while any other handle that refers to it is not yet closed; for example, database environment handles must not be closed while transactions in the environment have not yet been committed or aborted. Specifically, this includes the DB_TXN, DB_LOGC and DB_MPOOLFILE handles.

Where the environment was initialized with the DB_INIT_LOCK flag, calling DB_ENV->close() does not release any locks still held by the closing process, providing functionality for long-lived locks. Processes that want to have all their locks released can do so by issuing the appropriate DB_ENV->lock_vec() call.

Where the environment was initialized with the DB_INIT_MPOOL flag, calling DB_ENV->close() implies calls to DB_MPOOLFILE->close() for any remaining open files in the memory pool that were returned to this process by calls to DB_MPOOLFILE->open() . It does not imply a call to DB_MPOOLFILE->sync() for those files.

Where the environment was initialized with the DB_INIT_TXN flag, calling DB_ENV->close() aborts any unresolved transactions. Applications should not depend on this behavior for transactions involving Berkeley DB databases; all such transactions should be explicitly resolved. The problem with depending on this semantic is that aborting an unresolved transaction involving database operations requires a database handle. Because the database handles should have been closed before calling DB_ENV->close(), it will not be possible to abort the transaction, and recovery will have to be run on the Berkeley DB environment before further operations are done.

Where log cursors were created using the DB_ENV->log_cursor() method, calling DB_ENV->close() does not imply closing those cursors.

In multithreaded applications, only a single thread may call the DB_ENV->close() method.

After DB_ENV->close() has been called, regardless of its return, the Berkeley DB environment handle may not be accessed again.

The DB_ENV->close() method returns a non-zero error value on failure and 0 on success.



The flags parameter must be set to 0 or be set to one of the following values:


    When closing each database handle internally, synchronize the database. If this flag is not specified, the database handle is closed without synchronizing the database.


    When closing the enviroment, flush memory mapped environment regions to disk. Specifying this flag may help prevent loss of updates when __db.00* files are on NFS storage. However, there is a risk that this flag will significantly slow down this method call.



See Also

Database Environments and Related Methods