#include <db.h> int DB_TXN->prepare(DB_TXN *tid, u_int8_t gid[DB_GID_SIZE]);
         The DB_TXN->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 DB_TXN->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 DB_TXN->prepare() 
            
                  method returns a non-zero error value on failure and 0 on success.
            
            
        
         
         The errors that this method returns include the error values of DBcursor->close() and the following:
         
    
A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.
You attempted to open a database handle that is configured for no waiting exclusive locking, but the exclusive lock could not be immediately obtained. See DB->set_lk_exclusive() for more information.
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 DB_ENV->txn_recover() telling the application which global transactions must be resolved.