Communication for version management in a distributed information service

A method for locating and rendering inaccessible obsolete versions of data objects, the objects being utilized in multiple nodes of a distributed processing system in which at least one node operates as an object source location having access to a source database containing source data objects and at least one other node operates as an object replica location having means for storing versions of requested objects received from a source location, each source data object being alterable whereby a plurality of versions are created and versions stored at replica locations may become obsolete, the relative obsolescence of each version at any time t being identifiable by a version number corresponding to its position in a temporal sequence, including an oldest version and a most recent version, among versions of source data objects comprising the steps at each source location of:

• maintaining a list of replica locations;
• maintaining a list of identifiers of obsolete versions of source data objects for each identified replica location;
• responsive to a request at a time t.sub.1 from a first replica location to ascertain obsolescence of at least one data object, extracting from list of identifiers a first subset of identifiers corresponding to versions which have previously been sent to said first replica location, and extracting from the first subset of identifiers, a second subset of identifiers corresponding to versions which are oldest in said temporal sequence at time t.sub.1 ;
• sending the second subset of identifiers to said first replica location as one or more messages in an atomic demand/response sequence, any interruption in the sequence resulting in an abort;
• and
• responsive to an acknowledgment from the replica location, deleting the second subset of identifiers from the list of identifiers;
• and
• comprising the steps at said first replica location of:
• sending at least once to each source location employed by this replica location, a signal identifying this replica location;
• initiating a request to ascertain obsolescence of at least one data object from the source location;
• and
• upon receiving one or more messages from the source location, rendering inaccessible those versions of data objects identified by any one of the messages so received.

In a distributed processing system having a network of nodes connected by communication links in which at least one node of the system operates as a source location having access to a source database containing source data objects and at least one other node operates as a replica location having a means for storing replicas of source data objects received from a source location, an apparatus for managing obsolescence of replicas comprising:

• manager means, in communication with a source location, for maintaining obsolescence data identifying obsolete replicas;
• means at a requesting replica location for generating an invalidation request for at least a portion of the obsolescence data;
• and
• server means, in communication with the manager means and the requesting replica location and responsive to the invalidation request, for supplying the portion of the obsolescence data to the requesting replica location.