#include <db_cxx.h> int DbTxn::commit(u_int32_t flags);
The DbTxn::commit() method ends the transaction.
In the case of nested transactions, if the transaction is a parent transaction, committing the parent transaction causes all unresolved children of the parent to be committed. In the case of nested transactions, if the transaction is a child transaction, its locks are not released, but are acquired by its parent. Although the commit of the child transaction will succeed, the actual resolution of the child transaction is postponed until the parent transaction is committed or aborted; that is, if its parent transaction commits, it will be committed; and if its parent transaction aborts, it will be aborted.
All cursors opened within the transaction must be closed before the transaction is committed. If they are not closed, they will be closed by this function. When the close operation for a cursor fails, the method returns a non-zero error value for the first instance of such an error, closes the rest of the cursors, and then aborts the transaction.
After DbTxn::commit() has been called, regardless of its return, the
DbTxn handle may not be
accessed again. If DbTxn::commit() encounters an error, the
transaction and all child transactions of the transaction are aborted.
The DbTxn::commit()
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 errors values that this method returns include the error values of the
Dbc::close() method and the following:
A transactional database environment operation was selected to resolve a deadlock.
DbDeadlockException is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, DB_LOCK_DEADLOCK is returned.
A Berkeley DB Concurrent Data Store database environment configured for lock timeouts was unable to grant a lock in the allowed time.
DbLockNotGrantedException is thrown if
your Berkeley DB API is configured to throw exceptions.
Otherwise, DB_LOCK_NOTGRANTED is returned.
The flags parameter must be set to 0 or one of the following values:
DB_TXN_NOSYNC
Do not synchronously flush the log. 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() method or for a single transaction using the DbEnv::txn_begin() method. Any value specified to this method overrides both of those settings.
DB_TXN_SYNC
Synchronously flush the log. 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() method. This behavior may also be set for a single transaction using the DbEnv::txn_begin() method. Any value specified to this method overrides both of those settings.
DB_TXN_WRITE_NOSYNC
Write but do not synchronously flush the log on transaction commit. This means that transactions exhibit the ACI (atomicity, consistency, and isolation) properties, but not D (durability); that is, database integrity will be maintained, but if the system fails, it is possible some number of the most recently committed transactions may be undone during recovery. The number of transactions at risk is governed by how often the system flushes dirty buffers to disk and how often the log is checkpointed.
This form of commit protects you against application
crashes, but not against OS crashes. This method
offers less room for the possiblity of data loss than
does DB_TXN_NOSYNC.
This behavior may be set for a Berkeley DB environment using the DbEnv::set_flags() method or for a single transaction using the DbEnv::txn_begin() method. Any value specified to this method overrides both of those settings.