#include <db.h>

int
DB_TXN->prepare(DB_TXN *tid, u_int8_t gid[DB_XIDDATASIZE]);  

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.

The DB_TXN->prepare() method returns a non-zero error value on failure and 0 on success.