Overwriting data objects in a dispersed storage network

A processing system of a dispersed storage and task (DST) processing unit comprises:

• at least one processor;
• a memory that stores operational instructions, that when executed by the at least one processor cause the processing system to:
• determine to overwrite an original data object stored in a plurality of storage units with an updated data object, wherein the original data object includes a plurality of data regions, wherein each of the plurality of data regions includes a plurality of data segments, and wherein each of the plurality of data segments was dispersed storage error encoded to produce a set of encoded data slices stored in a set of storage units of the plurality of storage units;
• retrieve checksum metadata associated with the original data object in response to determining to overwrite an original data object, wherein the checksum metadata includes one object level checksum corresponding to the original data object, wherein the checksum metadata further includes a plurality of region level checksums corresponding to the plurality of data regions of the original data object, and wherein the checksum metadata further includes a plurality of segment level checksums corresponding to the plurality of data segments of the plurality of data regions;
• determine validation level data indicating one of:
• a data object overwrite level, a data region overwrite level, or a data segment overwrite level;
• when the validation level data indicates a data object overwrite level:
• extract an object level checksum from the checksum metadata;
• determine an object overwrite checksum value;
• generate object validation data by comparing the object overwrite checksum value to the object level checksum;
• facilitate performance of overwriting the original data object with the updated data object when the object validation data indicates the object overwrite checksum value compares unfavorably to the one object level checksum;
• and
• forego overwriting of the original data object when the object validation data indicates the object overwrite checksum value compares favorably to the object level checksum;
• when the validation level data indicates a data region overwrite level:
• extract a plurality of region level checksums from the checksum metadata, wherein the plurality of region level checksums corresponds to the plurality of data regions of the original data object;
• determine a plurality of region overwrite checksum values;
• generate region validation data by comparing each of the plurality of region level checksums to a corresponding one of the plurality of region overwrite checksum values, wherein the region validation data indicates a first subset of the plurality of data regions of the original data object, corresponding to a first subset of the plurality of region level checksums that compare unfavorably to a corresponding first subset of the plurality of region overwrite checksum values, wherein the region validation data indicates a second subset of the plurality of data regions of the original data object, corresponding to a second subset of the plurality of region level checksums that compare favorably to a corresponding second subset of the plurality of region overwrite checksum values, and wherein the first subset of the plurality of data regions and the second subset of the plurality of data regions are mutually exclusive and collectively exhaustive with respect to the plurality of data regions of the original data object;
• facilitate performance of overwriting the first subset of the plurality of data regions of the original data object with a corresponding first subset of a plurality of data regions of the updated data object;
• and
• forego overwriting of the second subset of the plurality of data regions of the original data object;
• and;
• when the validation level data indicates a data segment overwrite level:
• extract a plurality of segment level checksums from the checksum metadata, wherein the plurality of segment level checksums corresponds to the plurality of data segments of the original data object;
• determine a plurality of segment overwrite checksum values;
• generate segment validation data by comparing each of the plurality of segment level checksums to a corresponding one of the plurality of segment overwrite checksum values, wherein the segment validation data indicates a first subset of the plurality of data segments of the original data object, corresponding to a first subset of the plurality of segment level checksums that compare unfavorably to a corresponding first subset of the plurality of segment overwrite checksum values, wherein the segment validation data indicates a second subset of the plurality of data segments of the original data object, corresponding to a second subset of the plurality of segment level checksums that compare favorably to a corresponding second subset of the plurality of segment overwrite checksum values, and wherein the first subset of the plurality of data segments and the second subset of the plurality of data segments are mutually exclusive and collectively exhaustive with respect to the plurality of data segments of the original data object;
• facilitate performance of overwriting the first subset of the plurality of data segments of the original data object with a corresponding first subset of a plurality of data segments of the updated data object;
• and
• forego overwriting of the second subset of the plurality of data segments of the original data object.

A non-transitory computer readable storage medium comprises:

• at least one memory section that stores operational instructions that, when executed by a processing system of a dispersed storage network (DSN) that includes a processor and a memory, causes the processing system to:
• determine to overwrite an original data object stored in a plurality of storage units with an updated data object, wherein the original data object includes a plurality of data regions, wherein each of the plurality of data regions includes a plurality of data segments, and wherein each of the plurality of data segments was dispersed storage error encoded to produce a set of encoded data slices stored in a set of storage units of the plurality of storage units;
• retrieve checksum metadata associated with the original data object in response to determining to overwrite an original data object, wherein the checksum metadata includes one object level checksum corresponding to the original data object, wherein the checksum metadata further includes a plurality of region level checksums corresponding to the plurality of data regions of the original data object, and wherein the checksum metadata further includes a plurality of segment level checksums corresponding to the plurality of data segments of the plurality of data regions;
• determine validation level data indicating one of:
• a data object overwrite level, a data region overwrite level, or a data segment overwrite level;
• when the validation level data indicates a data object overwrite level:
• extract an object level checksum from the checksum metadata;
• determine an object overwrite checksum value;
• generate object validation data by comparing the object overwrite checksum value to the object level checksum;
• facilitate performance of overwriting the original data object with the updated data object when the object validation data indicates the object overwrite checksum value compares unfavorably to the one object level checksum;
• and
• forego overwriting of the original data object when the object validation data indicates the object overwrite checksum value compares favorably to the object level checksum;
• when the validation level data indicates a data region overwrite level:
• extract a plurality of region level checksums from the checksum metadata, wherein the plurality of region level checksums corresponds to the plurality of data regions of the original data object;
• determine a plurality of region overwrite checksum values;
• generate region validation data by comparing each of the plurality of region level checksums to a corresponding one of the plurality of region overwrite checksum values, wherein the region validation data indicates a first subset of the plurality of data regions of the original data object, corresponding to a first subset of the plurality of region level checksums that compare unfavorably to a corresponding first subset of the plurality of region overwrite checksum values, wherein the region validation data indicates a second subset of the plurality of data regions of the original data object, corresponding to a second subset of the plurality of region level checksums that compare favorably to a corresponding second subset of the plurality of region overwrite checksum values, and wherein the first subset of the plurality of data regions and the second subset of the plurality of data regions are mutually exclusive and collectively exhaustive with respect to the plurality of data regions of the original data object;
• facilitate performance of overwriting the first subset of the plurality of data regions of the original data object with a corresponding first subset of a plurality of data regions of the updated data object;
• and
• forego overwriting of the second subset of the plurality of data regions of the original data object;
• and;
• when the validation level data indicates a data segment overwrite level:
• extract a plurality of segment level checksums from the checksum metadata, wherein the plurality of segment level checksums corresponds to the plurality of data segments of the original data object;
• determine a plurality of segment overwrite checksum values;
• generate segment validation data by comparing each of the plurality of segment level checksums to a corresponding one of the plurality of segment overwrite checksum values, wherein the segment validation data indicates a first subset of the plurality of data segments of the original data object, corresponding to a first subset of the plurality of segment level checksums that compare unfavorably to a corresponding first subset of the plurality of segment overwrite checksum values, wherein the segment validation data indicates a second subset of the plurality of data segments of the original data object, corresponding to a second subset of the plurality of segment level checksums that compare favorably to a corresponding second subset of the plurality of segment overwrite checksum values, and wherein the first subset of the plurality of data segments and the second subset of the plurality of data segments are mutually exclusive and collectively exhaustive with respect to the plurality of data segments of the original data object;
• facilitate performance of overwriting the first subset of the plurality of data segments of the original data object with a corresponding first subset of a plurality of data segments of the updated data object;
• and
• forego overwriting of the second subset of the plurality of data segments of the original data object.