DbTxn::prepare()
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## DbTxn::prepare()

    #include <db_cxx.h>

    int
    DbTxn::prepare(u_int8_t gid[DB_GID_SIZE]);

The `DbTxn::prepare()` method initiates the beginning of a two-phase commit.

In a distributed transaction environment, Berkeley DB can be used as a local transaction manager. In this case, the distributed transaction manager must send prepare messages to each local manager. The local manager must then issue a `DbTxn::prepare()` and await its successful return before responding to the distributed transaction manager. Only after the distributed transaction manager receives successful responses from all of its prepare messages should it issue any commit messages.

In the case of nested transactions, preparing the parent causes all unresolved children of the parent transaction to be committed. Child transactions should never be explicitly prepared. Their fate will be resolved along with their parent's during global recovery.

All open cursors in the transaction are closed and the first cursor close error will be returned.

The `DbTxn::prepare()` 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 errors that this 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

#### gid

The gid parameter specifies the global transaction ID by which this transaction will be known. This global transaction ID will be returned in calls to DbEnv::txn_recover() telling the application which global transactions must be resolved.

### Class

DbEnv, DbTxn

### See Also

Transaction Subsystem and Related Methods

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