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From "Aman Sinha (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (DRILL-1946) Wrong result for aggregation query with lower slice_target
Date Sun, 25 Jan 2015 01:39:35 GMT

     [ https://issues.apache.org/jira/browse/DRILL-1946?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Aman Sinha resolved DRILL-1946.
-------------------------------
    Resolution: Duplicate

Closing as duplicate as per previous comment.  I will add a separate unit test for this. 

> Wrong result for aggregation query with lower slice_target
> ----------------------------------------------------------
>
>                 Key: DRILL-1946
>                 URL: https://issues.apache.org/jira/browse/DRILL-1946
>             Project: Apache Drill
>          Issue Type: Bug
>          Components: Query Planning & Optimization
>    Affects Versions: 0.7.0
>            Reporter: Aman Sinha
>            Assignee: Aman Sinha
>             Fix For: 0.8.0
>
>
> Here's the result with the default value of slice_target for the following query: 
> {code}
> select count(*) from (
> SELECT l_suppkey, sum(l_extendedprice)/sum(l_quantity)
> FROM cp.`tpch/lineitem.parquet`
> WHERE (l_orderkey in (SELECT o_orderkey FROM cp.`tpch/orders.parquet`
>                        WHERE o_custkey < 2) )
> GROUP BY l_suppkey
> );
> +------------+
> |   EXPR$0   |
> +------------+
> | 29         |
> +------------+
> {code}
> I lowered the slice_target in order to force exchanges in the following query.  The result
is wrong.   
> {code}
> 0: jdbc:drill:zk=local> alter session set `planner.slice_target` = 1;
> select count(*) from (
> SELECT l_suppkey, sum(l_extendedprice)/sum(l_quantity)
> FROM cp.`tpch/lineitem.parquet`
> WHERE (l_orderkey in (SELECT o_orderkey FROM cp.`tpch/orders.parquet`
>                        WHERE o_custkey < 2) )
> GROUP BY l_suppkey
> );
> +------------+
> |   EXPR$0   |
> +------------+
> | 14         |
> +------------+
> {code}
> The Explain plan for the second query has multiphase aggregates.  When I set planner.enable_multiphase_agg
= false, the result is correct, so it seems to be a multiphase aggregate issue based on a
preliminary analysis (although there might be other things going on). 



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