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Date: Thu, 8 Dec 2016 17:34:58 +0000 (UTC)
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Subject: [jira] [Commented] (FLINK-5226) Eagerly project unused attributes
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archived-at: Thu, 08 Dec 2016 17:35:00 -0000


    [ https://issues.apache.org/jira/browse/FLINK-5226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15732843#comment-15732843 ] 

ASF GitHub Bot commented on FLINK-5226:
---------------------------------------

Github user fhueske commented on the issue:

    https://github.com/apache/flink/pull/2926
  
    Merging


> Eagerly project unused attributes
> ---------------------------------
>
>                 Key: FLINK-5226
>                 URL: https://issues.apache.org/jira/browse/FLINK-5226
>             Project: Flink
>          Issue Type: Improvement
>          Components: Table API & SQL
>    Affects Versions: 1.2.0
>            Reporter: Fabian Hueske
>            Assignee: Fabian Hueske
>
> The optimizer does currently not eagerly remove unused attributes. 
> For example given a table {{tab5}} with five attributes {{a, b, c, d, e}}, the following query
> {code}
> SELECT x.a, y.b FROM tab5 AS x, tab5 AS y WHERE x.a = y.a
> {code}
> would result in the non-optimized plan
> {code}
> LogicalProject(a=[$0], b=[$6])
>   LogicalFilter(condition=[=($0, $5)])
>     LogicalJoin(condition=[true], joinType=[inner])
>       LogicalTableScan(table=[[tab5]])
>       LogicalTableScan(table=[[tab5]])
> {code}
> and the optimized plan:
> {code}
> DataSetCalc(select=[a, b0 AS b])
>   DataSetJoin(where=[=(a, a0)], join=[a, b, c, d, e, a0, b0, c0, d0, e0], joinType=[InnerJoin])
>     DataSetScan(table=[[_DataSetTable_0]])
>     DataSetScan(table=[[_DataSetTable_0]])
> {code}
> This plan is inefficient because it joins all ten attributes of both tables instead of eagerly projecting out all unused fields ({{x.b, x.c, x.d, x.e, y.c, y.d, y.e}}).
> Since this is one of the most common optimizations, I would assume that Calcite provides some rules to extract eager projections. If this is the case, the issue can be solved by adding such rules to {{FlinkRuleSets}}.


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