Bankim Bhavsar created KUDU-3286:
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Summary: 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
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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