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From "Pradeep Kamath (JIRA)" <>
Subject [jira] [Commented] (HIVE-3733) Improve Hive's logic for conditional merge
Date Fri, 30 Nov 2012 03:01:58 GMT


Pradeep Kamath commented on HIVE-3733:

Re-running testCliDriver_groupby_multi_single_reducer locally I noticed it is failing because
the new code is adding an additional conditional merge. The query is a multi insert one but
all with map-reduce phases - so it appears like this is a regression.

In the debugger I noticed:
currWork.getReducer() is org.apache.hadoop.hive.ql.exec.ExtractOperator@66bb4c22
However stack does not contain it causing the merge operation to be added!
Stack has:
[org.apache.hadoop.hive.ql.exec.TableScanOperator@476acffa, org.apache.hadoop.hive.ql.exec.SelectOperator@3de76262,
org.apache.hadoop.hive.ql.exec.ReduceSinkOperator@61607dda, org.apache.hadoop.hive.ql.exec.ForwardOperator@5e6a528,
org.apache.hadoop.hive.ql.exec.FilterOperator@1b97680c, org.apache.hadoop.hive.ql.exec.GroupByOperator@712ff9fa,
org.apache.hadoop.hive.ql.exec.SelectOperator@433d44fc, org.apache.hadoop.hive.ql.exec.SelectOperator@2c3b39be,

Any ideas why this is happening?
> Improve Hive's logic for conditional merge
> ------------------------------------------
>                 Key: HIVE-3733
>                 URL:
>             Project: Hive
>          Issue Type: Improvement
>            Reporter: Pradeep Kamath
>            Assignee: Pradeep Kamath
>         Attachments: HIVE-3733.1.patch.txt, HIVE-3733.3.patch.txt
> If the config hive.merge.mapfiles is set to true and hive.merge.mapredfiles is set to
false then when hive encounters a FileSinkOperator when generating map reduce tasks, it will
look at the entire job to see if it has a reducer, if it does it will not merge. Instead it
should be check if the FileSinkOperator is a child of the reducer. This means that outputs
generated in the mapper will be merged, and outputs generated in the reducer will not be,
the intended effect of setting those configs.
> Simple repro:
> set hive.merge.mapfiles=true;
> set hive.merge.mapredfiles=false;
> FROM <input_table>
> INSERT OVERWRITE TABLE <output_table1> SELECT key, COUNT(*) group by key
> The output should contain a Conditional Operator, Mapred Stages, and Move tasks

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