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From Tsuyoshi Ozawa <oz...@apache.org>
Subject TimSort bug and its workaround
Date Thu, 26 Feb 2015 08:04:05 GMT
Hi hadoop developers,

Last 2 weeks, a bug of JDK about TimSort, related to Collections#sort,
 is reported. How can we deal with this problem?

http://envisage-project.eu/timsort-specification-and-verification/
https://bugs.openjdk.java.net/browse/JDK-8072909

The bug causes ArrayIndexOutOfBoundsException if the number of element
is larger than 67108864.

We use the sort method at 77 places at least.
find . -name "*.java" | xargs grep "Collections.sort"  | wc -l
77

One reasonable workaround is to set
java.util.Arrays.useLegacyMergeSort() by default.

Thanks,
- Tsuyoshi

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