Db::close()
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## Db::close()

    #include <db_cxx.h>

    int
    Db::close(u_int32_t flags);

The `Db::close()` method flushes cached database information to disk, closes any open cursors, frees allocated resources, and closes underlying files. When the close operation for a cursor 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 cursors and database handles.

Although closing a database handle will close any open cursors, it is recommended that applications explicitly close all their Dbc handles before closing the database. The reason why is that when the cursor is explicitly closed, the memory allocated for it is reclaimed; however, this will not happen if you close a database while cursors are still opened.

The same rule, for the same reasons, hold true for DbTxn handles. Simply make sure you close all your transaction handles before closing your database handle.

Because key/data pairs are cached in memory, applications should make a point to always either close database handles or sync their data to disk (using the Db::sync() method) before exiting, to ensure that any data cached in main memory are reflected in the underlying file system.

When called on a database that is the primary database for a secondary index, the primary database should be closed only after all secondary indices referencing it have been closed.

When multiple threads are using the Db concurrently, only a single thread may call the `Db::close()` method.

The Db handle may not be accessed again after `Db::close()` is called, regardless of its return.

If you do not close the Db handle explicitly, it will be closed when the environment handle that owns the Db handle is closed.

The `Db::close()` method either returns a non-zero error value or throws an exception that encapsulates a non-zero error value on failure, and returns 0 on success. The error values that `Db::close()` method returns include the error values of `Dbc::close()` and the following:

#### DbDeadlockException or DB_LOCK_DEADLOCK

A transactional database environment operation was selected to resolve a deadlock.

DbDeadlockException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_DEADLOCK` is returned.

#### DbLockNotGrantedException or DB_LOCK_NOTGRANTED

A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.

DbLockNotGrantedException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_NOTGRANTED` is returned.

#### EINVAL

If the cursor is already closed; or if an invalid flag value or parameter was specified.

### Parameters

#### flags

The flags parameter must be set to 0 or be set to the following value:

- `DB_NOSYNC`

  Do not flush cached information to disk. This flag is a dangerous option. It should be set only if the application is doing logging (with transactions) so that the database is recoverable after a system or application crash, or if the database is always generated from scratch after any system or application crash.

  It is important to understand that flushing cached information to disk only minimizes the window of opportunity for corrupted data. Although unlikely, it is possible for database corruption to happen if a system or application crash occurs while writing data to the database. To ensure that database corruption never occurs, applications must either: use transactions and logging with automatic recovery; use logging and application-specific recovery; or edit a copy of the database, and once all applications using the database have successfully called `Db::close()`, atomically replace the original database with the updated copy.

  Note that this flag only works when the database has been opened using an environment.

### Errors

The `Db::close()` method may fail and throw a DbException exception, encapsulating one of the following non-zero errors, or return one of the following non-zero errors:

#### EINVAL

An invalid flag value or parameter was specified.

The error messages returned for the first error encountered when `Db::close()` method closes any open cursors include:

#### DbDeadlockException or DB_LOCK_DEADLOCK

A transactional database environment operation was selected to resolve a deadlock.

DbDeadlockException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_DEADLOCK` is returned.

#### DbLockNotGrantedException or DB_LOCK_NOTGRANTED

A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.

DbLockNotGrantedException is thrown if your Berkeley DB API is configured to throw exceptions. Otherwise, `DB_LOCK_NOTGRANTED` is returned.

#### EINVAL

If the cursor is already closed; or if an invalid flag value or parameter was specified.

### Class

Db

### See Also

Database and Related Methods

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