# DbTxn::prepare

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    #include <db_cxx.h>

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

# Description

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 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.

# Errors

The DbTxn::prepare method may fail and throw an exception or return a non-zero error 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 either return DB_RUNRECOVERY or throw an exception encapsulating DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.

# Class

DbEnv, DbTxn

# See Also

DbEnv::set_tx_max, DbEnv::set_tx_recover, DbEnv::set_tx_timestamp, DbTxn::abort, DbEnv::txn_begin, DbEnv::txn_checkpoint, DbTxn::commit, DbTxn::discard, DbTxn::id, DbTxn::prepare, DbEnv::txn_recover, DbTxn::set_timeout and DbEnv::txn_stat.`

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