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https://issues.apache.org/jira/browse/KUDU-3286?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17347080#comment-17347080
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Bankim Bhavsar commented on KUDU-3286:
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This issue has been fixed for upcoming 1.15.0 release with commit bd27769
[https://gerrit.cloudera.org/c/17470/
]
This commit required introducing a feature flag that makes Kudu client < 1.15.0
incompatible with server >= 1.15.0 and vice-versa. Impala the main consumer of
this feature will be bumping up its kudu client to be compatible.
> Add special handling for empty strings for Bloom filter predicate push down
> ---------------------------------------------------------------------------
>
> Key: KUDU-3286
> URL: https://issues.apache.org/jira/browse/KUDU-3286
> Project: Kudu
> Issue Type: Improvement
> Affects Versions: 1.13.0
> Reporter: Bankim Bhavsar
> Assignee: Bankim Bhavsar
> Priority: Major
>
> Fast hash used with Bloom filter predicate pushdown has special handling for
> nullptr.
> [https://github.com/apache/kudu/blob/master/src/kudu/util/hash_util.h#L95]
> However there isn't any special handling for empty objects/strings. Fast hash
> for an empty string with seed=0 generates a hash value of 0. This doesn't set
> any bits in Bloom filter and as a result empty strings are reported as not
> present.
> Impala uses the direct bloom filter approach and includes special handling
> for empty strings.
> [https://github.com/apache/impala/blob/master/be/src/runtime/raw-value.inline.h#L352]
> This leads to discrepancy between Impala and Kudu and returns incorrect join
> results.
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