public void prepare(byte gid) throws DbException;
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.
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. The gid parameter must be sized at least Db.DB_XIDDATASIZE (currently 128) bytes; only the first Db.DB_XIDDATASIZE bytes are used.
The DbTxn.prepare method throws an exception that encapsulates a non-zero error value on failure.
The DbTxn.prepare method may fail and throw an exception for errors specified for other Berkeley DB and C library or system methods. If a catastrophic error has occurred, the DbTxn.prepare method may fail and throw a DbRunRecoveryException, in which case all subsequent Berkeley DB calls will fail in the same way.
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