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
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
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.
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 a
in which case all subsequent Berkeley DB calls will fail in the same way.
Transaction Subsystem and Related Methods
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