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https://issues.apache.org/jira/browse/HIVE-9495?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Anand Sridharan reassigned HIVE-9495:
-------------------------------------
Assignee: Anand Sridharan
> Map Side aggregation affecting map performance
> ----------------------------------------------
>
> Key: HIVE-9495
> URL: https://issues.apache.org/jira/browse/HIVE-9495
> Project: Hive
> Issue Type: Bug
> Components: Query Processor
> Affects Versions: 0.14.0
> Environment: RHEL 6.4
> Hortonworks Hadoop 2.2
> Reporter: Anand Sridharan
> Assignee: Anand Sridharan
> Attachments: HIVE-9495.1.patch.txt, HIVE-9495.2.patch.txt,
> profiler_screenshot.PNG
>
>
> When trying to run a simple aggregation query with hive.map.aggr=true, map
> tasks take a lot of time in Hive 0.14 as against with hive.map.aggr=false.
> e.g.
> Consider the query:
> {code}
> INSERT OVERWRITE TABLE lineitem_tgt_agg
> select alias.a0 as a0,
> alias.a2 as a1,
> alias.a1 as a2,
> alias.a3 as a3,
> alias.a4 as a4
> from (
> select alias.a0 as a0,
> SUM(alias.a1) as a1,
> SUM(alias.a2) as a2,
> SUM(alias.a3) as a3,
> SUM(alias.a4) as a4
> from (
> select lineitem_sf500.l_orderkey as a0,
> CAST(lineitem_sf500.l_quantity * lineitem_sf500.l_extendedprice * (1 -
> lineitem_sf500.l_discount) * (1 + lineitem_sf500.l_tax) as double) as a1,
> lineitem_sf500.l_quantity as a2,
> CAST(lineitem_sf500.l_quantity * lineitem_sf500.l_extendedprice *
> lineitem_sf500.l_discount as double) as a3,
> CAST(lineitem_sf500.l_quantity * lineitem_sf500.l_extendedprice *
> lineitem_sf500.l_tax as double) as a4
> from lineitem_sf500
> ) alias
> group by alias.a0
> ) alias;
> {code}
> The above query was run with ~376GB of data / ~3billion records in the source.
> It takes ~10 minutes with hive.map.aggr=false.
> With map side aggregation set to true, the map tasks don't complete even
> after an hour.
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