mboehm7 opened a new pull request #927: URL: https://github.com/apache/systemml/pull/927
This patch fixes remaining issues of incorrect results for colMins and colMaxs over compressed matrix blocks with shared DDC1 dictionaries. Specifically, if the individual column groups have only partial overlap, the shared dictionary contains a superset of column group distinct values. Since aggregation functions like min and max are executed only over the dictionary (without touching the compressed data), it led to incorrect results as we find extreme values that do not actually exist in the column group. Three alternatives approaches could solve this: (1) drop shared dictionaries, (2) execute colMins and colMaxs over the compressed data, or (3) refactor the double array dictionary into a proper class hierarchy and maintain additional meta data for shared dictionaries. We decided for (3) in order to keep predictable performance, irrespective of shared dictionaries and because this class hierarchy allows for further improvements of shared dictionaries between any subsets of column groups. Additionally, this fix also cleanups incorrect estimates of the individual column groups (because getValueSize was used in the estimates as a number of values, although it gave the size in bytes) as well as some of the Class-layout size estimation tests. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
