Fabian Hueske created FLINK-1664:
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Summary: Fix sorting on POJO fields
Key: FLINK-1664
URL: https://issues.apache.org/jira/browse/FLINK-1664
Project: Flink
Issue Type: Bug
Components: JobManager
Affects Versions: 0.8.0, 0.9
Reporter: Fabian Hueske
Flink's groupSort, partitionSort, and outputSort operators allow to sort
partitions or groups of a DataSet.
If the sort is defined on a POJO field, the sort order is not well defined.
Internally, the POJO is recursively decomposed into atomic fields (primitives
or generic types) and sorted by sorting these atomic fields. Thereby, the order
of these atomic fields is not well defined (I believe it is lexicographic order
of the POJO's member names).
IMO, the best approach is to forbid sorting on POJO types for now. Instead, it
is always possible to select the nested fields of the POJO that should be used
for sorting. Later we can relax this restriction.
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