int DB_ENV->txn_begin(DB_ENV *env, DB_TXN *parent, DB_TXN **tid, u_int32_t flags);
The DB_ENV->txn_begin method creates a new transaction in the environment and copies a pointer to a DB_TXN that uniquely identifies it into the memory to which tid refers. Calling the DB_TXN->abort, DB_TXN->commit or DB_TXN->discard methods will discard the returned handle.
If the parent argument is non-NULL, the new transaction will be a nested transaction, with the transaction indicated by parent as its parent. Transactions may be nested to any level. In the presence of distributed transactions and two-phase commit, only the parental transaction, that is a transaction without a parent specified, should be passed as an argument to DB_TXN->prepare.
The flags value must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values:
This behavior may be set for a Berkeley DB environment using the DB_ENV->set_flags interface. Any value specified in this interface overrides that setting.
This behavior is the default for Berkeley DB environments unless the DB_TXN_NOSYNC flag was specified to the DB_ENV->set_flags interface. Any value specified in this interface overrides that setting.
Note: A transaction may not span threads; that is, each transaction must begin and end in the same thread, and each transaction may be used only by a single thread.
Note: Cursors may not span transactions; that is, each cursor must be opened and closed within a single transaction.
Note: A parent transaction may not issue any Berkeley DB operations -- except for DB_ENV->txn_begin, DB_TXN->abort and DB_TXN->commit -- while it has active child transactions (child transactions that have not yet been committed or aborted).
The DB_ENV->txn_begin method returns a non-zero error value on failure and 0 on success.
The DB_ENV->txn_begin method may fail and return a non-zero error for the following conditions:
The DB_ENV->txn_begin method may fail and return a non-zero error for errors specified for other Berkeley DB and C library or system functions. If a catastrophic error has occurred, the DB_ENV->txn_begin method may fail and return DB_RUNRECOVERY, in which case all subsequent Berkeley DB calls will fail in the same way.
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