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From "Aman Sinha (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DRILL-1946) Wrong result for aggregation query with lower slice_target
Date Sun, 25 Jan 2015 01:37:34 GMT

    [ https://issues.apache.org/jira/browse/DRILL-1946?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14290935#comment-14290935
] 

Aman Sinha commented on DRILL-1946:
-----------------------------------

The fix for DRILL-2063 (ensure uniqueness of fields in output row type of an AggregateRel)
also fixes the wrong result for this issue.  Lowering the slice_target forces multiphase aggregate
which also affects the field references from the 2nd phase aggregate to its child operators,
so it seems reasonable that the root cause of both issues is the same. 

> 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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