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From "Gabriel Reid (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CRUNCH-528) Pair: Integer overflow during comparison can cause inconsistent sort.
Date Wed, 27 May 2015 18:28:17 GMT

    [ https://issues.apache.org/jira/browse/CRUNCH-528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14561437#comment-14561437
] 

Gabriel Reid commented on CRUNCH-528:
-------------------------------------

Nice catch [~bvargo]! Patch looks good, but I just noticed that there is another minor issue
with Pair.cmp, in that it uses identity instead of equality at first to compare lhs and rhs.
I'll just do a tiny little addendum to your patch before I commit it.

> Pair: Integer overflow during comparison can cause inconsistent sort.
> ---------------------------------------------------------------------
>
>                 Key: CRUNCH-528
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-528
>             Project: Crunch
>          Issue Type: Bug
>          Components: Core
>            Reporter: Brandon Vargo
>            Assignee: Josh Wills
>            Priority: Minor
>         Attachments: 0001-Pair-Fix-comparison-for-large-hash-codes.patch
>
>
> Pair uses the hash code of each value for comparison if the values are not themselves
comparable. If the hash code values are too large, then the values will wrap when doing subtraction.
This results in a comparison function that is not transitive.
> Among other things, this makes Joins using the in-memory pipeline not work, since the
in-memory shuffler uses a TreeMap if the key type is Comparable. Since the key in a join is
a Pair of the original key and a join tag, the key is always comparable. With a non-transitive
comparison function, it is possible for the two join tags of the original key to sort differently,
resulting in the two join tags not being adjacent for the original key. This results either
in either the cross product erroneously producing no values in the case of an inner join,
since the two join tags are not adjacent, or null values appearing when they should not in
the case of an outer join.
> As a workaround, ensure that the key used in a Join is comparable.



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