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https://issues.apache.org/jira/browse/HIVE-24234?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17209131#comment-17209131
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Mustafa Iman commented on HIVE-24234:
-------------------------------------
[~rajesh.balamohan]
Change makes sense to me. One thing I want to clarify is definition of
hive.map.aggr.hash.min.reduction config option. Its definition is the following
HIVEMAPAGGRHASHMINREDUCTION("hive.map.aggr.hash.min.reduction", (float) 0.99,
"Hash aggregation will be turned off if the ratio between hash table size and
input rows is bigger than this number. \n" +
"Set to 1 to make sure hash aggregation is never turned off."),
With new code, setting this value to 1 does not guarantee hash aggregation is
never turned off. (outputRecords) / (inputRecords * 1.0f) can be larger than 1
when grouping sets are present. Can you update the description of the config
option accordingly?
> Improve checkHashModeEfficiency in VectorGroupByOperator
> --------------------------------------------------------
>
> Key: HIVE-24234
> URL: https://issues.apache.org/jira/browse/HIVE-24234
> Project: Hive
> Issue Type: Improvement
> Reporter: Rajesh Balamohan
> Priority: Major
> Attachments: HIVE-24234.wip.patch
>
>
> Currently, {{VectorGroupByOperator::checkHashModeEfficiency}} compares the
> number of entries with the number input records that have been processed. For
> grouping sets, it accounts for grouping set length as well.
> Issue is that, the condition becomes invalid after processing large number of
> input records. This prevents the system from switching over to streaming
> mode.
> e.g Assume 500,000 input records processed, with 9 grouping sets, with
> 100,000 entries in hashtable. Hashtable would never cross 4,500,0000 entries
> as the max size itself is 1M by default.
> It would be good to compare the input records (adjusted for grouping sets)
> with number of output records (along with size of hashtable size) to
> determine hashing or streaming mode.
> E.g Q67.
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