Importance

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Abstract

A data storage system receives sets of the revisions such that each set of revisions changes the dataset from one consistent state to another. Each set of revisions is processed in a write-selected phase followed by a read-selected phase. In the write-selected phase, the revisions in each set are written to a buffer and processed to produce a directory of the set of revisions. In the read-selected phase, the revisions are read from the buffer and integrated into the dataset. When one set of revisions is in the read-selected phase, the next set of revisions is in the write-selected phase. To permit uninterrupted read-only access to a consistent state of the dataset, the data storage system responds to a request for reading specified data on a priority basis by first accessing the directory of the read-selected revisions to determine whether the specified data are in the read-selected set of revisions, and if so, the specified data are read from the read-selected set of revisions, and if not, the specified data are read from the dataset. In a preferred implementation, the sets of revisions are alternately written to either a first buffer or a second buffer, and processing of each set of revisions is switched from the write-selected phase to the read-selected phase by switching between the two buffers.

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First Claim