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https://issues.apache.org/jira/browse/HIVE-10349?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14497412#comment-14497412
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Sergey Shelukhin commented on HIVE-10349:
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[~hagleitn] [~prasanth_j] [~mmokhtar] [~gopalv] many queries in TPCDS suffer
from the problem where there are 1000s of reducers (sometimes, 3 stages of
600-700 reducers each); this is running on 6 nodes with ~6 slots each. Not sure
if this is caused just by the stats problem or there are other problems with
physical optimizer, but it seems like a big perf issue that we should address
soon.
> overflow in stats
> -----------------
>
> Key: HIVE-10349
> URL: https://issues.apache.org/jira/browse/HIVE-10349
> Project: Hive
> Issue Type: Bug
> Reporter: Sergey Shelukhin
> Assignee: Prasanth Jayachandran
>
> Discovered while running q17 in LLAP.
> {noformat}
> Reducer 2
> Execution mode: llap
> Reduce Operator Tree:
> Merge Join Operator
> condition map:
> Inner Join 0 to 1
> keys:
> 0 _col28 (type: int), _col27 (type: int)
> 1 cs_bill_customer_sk (type: int), cs_item_sk (type: int)
> outputColumnNames: _col1, _col2, _col6, _col8, _col9, _col22,
> _col27, _col28, _col34, _col35, _col45, _col51, _col63, _col66, _col82
> Statistics: Num rows: 1047651367827495040 Data size:
> 9223372036854775807 Basic stats: COMPLETE Column stats: PARTIAL
> Map Join Operator
> condition map:
> Inner Join 0 to 1
> keys:
> 0 _col22 (type: int)
> 1 d_date_sk (type: int)
> outputColumnNames: _col1, _col2, _col6, _col8, _col9,
> _col22, _col27, _col28, _col34, _col35, _col45, _col51, _col63, _col66,
> _col82, _col86
> input vertices:
> 1 Map 7
> Statistics: Num rows: 1152416529588199552 Data size:
> 9223372036854775807 Basic stats: COMPLETE Column stats: NONE
> {noformat}
> Data size overflows and row count also looks wrong. I wonder if this is why
> it generates 1009 reducers for this stage on 6 machines
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