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https://issues.apache.org/jira/browse/HIVE-10163?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14388188#comment-14388188
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Gopal V commented on HIVE-10163:
--------------------------------
{{WritableComparator::get()}} --> {{ReflectionUtils.setConf()}} is pointless,
but it misses the static synchronized block inside HADOOP-11771 because the
default argument is NULL.
There is no difference between each iteration of the same row-keys, since the
schema does not vary between JOIN keys in the same operator.
> CommonMergeJoinOperator calls WritableComparator.get() in the inner loop
> ------------------------------------------------------------------------
>
> Key: HIVE-10163
> URL: https://issues.apache.org/jira/browse/HIVE-10163
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 1.2.0
> Reporter: Gopal V
> Labels: JOIN, Performance
>
> The CommonMergeJoinOperator wastes CPU looking up the correct comparator for
> each WritableComparable in each row.
> {code}
> @SuppressWarnings("rawtypes")
> private int compareKeys(List<Object> k1, List<Object> k2) {
> int ret = 0;
> ....
> ret = WritableComparator.get(key_1.getClass()).compare(key_1, key_2);
> if (ret != 0) {
> return ret;
> }
> }
> {code}
> The slow part of that get() is deep within {{ReflectionUtils.setConf}}, where
> it tries to use reflection to set the Comparator config for each row being
> compared.
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