Field level replication method

Abstract

In a distributed computing system in which replicas of a document are separately stored and revised, the document containing data arranged in a number of fields, a method for replicating data contained in a revised document replica to the other of the replicas by replicating only the field or fields which have been revised since an earlier replication. The method includes the steps of dynamically maintaining a two byte document sequence number for each of the document replicas representing the number of revisions made to the replicas, and dynamically maintaining a one byte field sequence number for each of the fields in the replicas. The field sequence numbers for revised fields are set equal to the lower byte of the current document sequence number. When a replication is desired, the method involves determining which of the document replicas is more recently revised, determining which of the fields in the more recently revised replica are more recently revised than the corresponding fields in the other replica based on some or all of the field and document sequence numbers, and replicating only the data contained in each more recently revised fields to the corresponding fields in the other replica. The system can handle document sequence numbers greater than 256, in which field sequence numbers can no longer be accurately represented by one byte, by artificially incrementing field sequence numbers for unrevised fields and interpreting all field sequence numbers as having a value within 256 of the document sequence number.

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