A data processing system participating in two-phase transaction processing operations
which, when a system failure occurs while one or more transactions are in process,
can successfully rebuild "in-doubt" states even when another system failure occurs
during an attempt to effect the rebuild. The system includes a file management
system having exclusive access to reserved locations in the memory for reading
and writing meta-data therein and physical file access logic selectively coupling
the memory and the database access application, the physical file access logic
incorporating file protections which are controlled by the file management system;
such that, in the event of a failure, the local state of the transaction can be
faithfully rebuilt after restart by accessing the meta-data. Upon restart after
a failure, the results of incomplete non-"in-doubt" transactions are removed, the
files which have been updated by "in-doubt" transactions are locked and normal
access to the affected database is then permitted.
