#include <DbXml.hpp>

XmlTransaction XmlTransaction::createChild(u_int32_t flags = 0)

The XmlTransaction::createChild method creates a child transaction of this transaction. While this child transaction is active (has been neither committed nor aborted), the parent transaction may not issue any operations except for XmlTransaction::commit or XmlTransaction::abort.

• The flags parameter must be set to 0 or by bitwise inclusively OR'ing together one or more of the following values:
  DB_READ_COMMITTED
  • This operation will have degree 2 isolation. This provides for cursor stability but not repeatable reads. Data items which have been previously read by this transaction may be deleted or modified by other transactions before this transaction completes.
  DB_READ_UNCOMMITTED
  • This operation will support degree 1 isolation; that is, read operations may return data that has been modified by other transactions but which has not yet been committed. Silently ignored if the DB_READ_UNCOMMITTED flag was not specified when the underlying container was opened.
  DB_TXN_NOSYNC
  • Do not synchronously flush the log when this transaction commits or prepares. This means the transaction will exhibit the ACI (atomic, consistent, and isolated) properties, but not D (durable); 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 UNREF==dbenv_set_flags method. Any value specified to this method overrides that setting.

  DB_TXN_NOWAIT
  • If a lock is unavailable for any Berkeley DB operation performed in the context of this transaction, cause the operation to return DB_LOCK_DEADLOCK or throw an XmlException with DB error code DB_LOCK_DEADLOCK immediately instead of blocking on the lock.
  DB_TXN_SNAPSHOT
  • This transaction will execute with snapshot isolation. For containers with the DB_MULTIVERSION flag set, data values will be read as they are when the transaction begins, without taking read locks. Silently ignored for operations on databases with DB_MULTIVERSION not set on the underlying container (read locks are acquired).

    The error DB_LOCK_DEADLOCK will be returned from update operations if a snapshot transaction attempts to update data which was modified after the snapshot transaction read it.

  DB_TXN_SYNC
  • Synchronously flush the log when this transaction commits or prepares. This means the transaction will exhibit all of the ACID (atomic, consistent, isolated, and durable) properties.

    This behavior is the default for Berkeley DB environments unless the DB_TXN_NOSYNC flag was specified to the UNREF==dbenv_set_flags method. Any value specified to this method overrides that setting.