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From "Prasanth J (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HIVE-6707) LazyMap and LazyBinaryMap is broken
Date Thu, 20 Mar 2014 07:24:43 GMT
Prasanth J created HIVE-6707:
--------------------------------

             Summary: LazyMap and LazyBinaryMap is broken
                 Key: HIVE-6707
                 URL: https://issues.apache.org/jira/browse/HIVE-6707
             Project: Hive
          Issue Type: Bug
          Components: Serializers/Deserializers
    Affects Versions: 0.12.0, 0.11.0, 0.10.0, 0.9.0, 0.8.0, 0.7.0, 0.6.0, 0.5.0, 0.13.0
            Reporter: Prasanth J
            Assignee: Prasanth J
            Priority: Critical
             Fix For: 0.13.0, 0.14.0


LazyPrimitive and LazyBinaryPrimitive overrides hashcode method in HIVE-949. But it failed
to override equals() method. As a result, LazyMap and LazyBinaryMap will end up having multiple
values for the same key. Both LazyMap and LazyBinaryMap uses LinkedHashMap, so the expected
behaviour is to have a single value per unique key.

In the following code from LazyMap (LazyBinaryMap also has same code segment)
{code}
LazyPrimitive<?, ?> lazyKey = uncheckedGetKey(i);
if (lazyKey == null) {
  continue;
}
Object key = lazyKey.getObject();
if (key != null && !cachedMap.containsKey(key)) {
{code}

lazyKey.hashcode() returns the writable object's hashcode. The containsKeys() method of hash
map (http://grepcode.com/file/repository.grepcode.com/java/root/jdk/openjdk/6-b14/java/util/HashMap.java#366)
checks if the hashcode are same, if so then it uses equals() method to verify if the key already
exists. Since LazyPrimitive does not override equals() method it falls back to use Object
equals(). Object equals() will return true only if both object are exactly the same (this
== obj).
So in the above code segment, even if the key already exists, the new value will be inserted
with hash collision resulting in more number of map entries.



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