DbEnv::txn_begin(DbTxn *parent, DbTxn **tid, u_int32_t flags);
The DbEnv::txn_begin method creates a new transaction in the environment
and copies a pointer to a DbTxn that uniquely identifies it into
the memory to which tid refers.
Calling the DbTxn::abort,
DbTxn::commit or DbTxn::discard methods will discard the returned
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
The flags value must be set to 0 or by bitwise inclusively OR'ing together one or
more of the following values:
- All read operations performed by the transaction will read modified but
not yet committed data. Silently ignored if the DB_DIRTY_READ
flag was not specified when the underlying database was opened.
- Do not synchronously flush the log when this transaction commits or
prepares. This means the transaction will exhibit the ACI (atomicity,
consistency, and isolation) properties, but not D (durability); that is,
database integrity will be maintained but it is possible that this
transaction may be undone during recovery.
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.
- If a lock is unavailable for any Berkeley DB operation performed in the context
of this transaction,
return DB_LOCK_NOTGRANTED or throw a
immediately instead of blocking on the lock.
- Synchronously flush the log when this transaction commits or prepares.
This means the transaction will exhibit all of the ACID (atomicity,
consistency, isolation, and durability) properties.
This behavior is the default for Berkeley DB environments unless the
DB_TXN_NOSYNC flag was specified to the DbEnv::set_flags
interface. Any value specified in this interface overrides that
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 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 DbEnv::txn_begin method may fail and throw an exception or return a non-zero error for the following conditions:
- The maximum number of concurrent transactions has been reached.
The DbEnv::txn_begin 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 DbEnv::txn_begin 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
Copyright Sleepycat Software