[jira] [Created] (FLINK-39677) ARRAY_SORT fails at runtime with "Comparison method violates its general contract!" on arrays with duplicate elements

["Jim Hughes (Jira)" <ji...@apache.org>]

Jim Hughes created FLINK-39677:
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             Summary: ARRAY_SORT fails at runtime with "Comparison method violates its general contract!" on arrays with duplicate elements
                 Key: FLINK-39677
                 URL: https://issues.apache.org/jira/browse/FLINK-39677
             Project: Flink
          Issue Type: Bug
    Affects Versions: 2.2.1, 2.0.2, 2.1.2, 1.20.4, 2.3.0
            Reporter: Jim Hughes


*Title:* ARRAY_SORT fails at runtime with "Comparison method violates its general contract!" on arrays with duplicate elements

*Affects Versions:* 2.0 and earlier (wherever {{ArraySortFunction}} exists)

h3. Description

{{ArraySortFunction.ArraySortComparator.compare}} is built from a single SQL {{>}} evaluator and returns {{+1}} or {{-1}} based on the boolean result — it never returns {{0}}. For two equal elements {{a}} and {{b}}, both {{a > b}} and {{b > a}} are {{FALSE}}, so {{compare(a, b) == compare(b, a) == -1}}. This violates {{java.util.Comparator}}'s antisymmetry requirement.

TimSort detects the contradiction once the array is large enough to take the merge path (≥32 elements with duplicates), throwing:

{noformat}
java.lang.IllegalArgumentException: Comparison method violates its general contract!
    at java.util.TimSort.mergeHi(TimSort.java:903)
    at java.util.Arrays.sort(Arrays.java:1234)
    at org.apache.flink.table.runtime.functions.scalar.ArraySortFunction.eval(ArraySortFunction.java:91)
{noformat}




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