public DbTxn txn_begin(DbTxn parent, int flags) throws DbException;
The DbEnv.txn_begin method creates a new transaction in the environment and returns a DbTxn that uniquely identifies it.
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 DbTxn.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 DbEnv.set_flags interface. Any value specified in this interface overrides that setting.
This behavior is the default for Berkeley DB environments unless the Db.DB_TXN_NOSYNC flag was specified to the DbEnv.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 DbEnv.txn_begin, DbTxn.abort and DbTxn.commit -- while it has active child transactions (child transactions that have not yet been committed or aborted).
The DbEnv.txn_begin method throws an exception that encapsulates a non-zero error value on failure.
The DbEnv.txn_begin method may fail and throw an exception encapsulating a non-zero error for the following conditions:
The DbEnv.txn_begin 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 DbEnv.txn_begin 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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