[
https://issues.apache.org/jira/browse/FLINK-5226?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15731343#comment-15731343
]
ASF GitHub Bot commented on FLINK-5226:
---------------------------------------
Github user beyond1920 commented on a diff in the pull request:
https://github.com/apache/flink/pull/2926#discussion_r91455098
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/api/table/plan/nodes/dataset/DataSetCalc.scala
---
@@ -73,7 +75,11 @@ class DataSetCalc(
val child = this.getInput
val rowCnt = metadata.getRowCount(child)
- val exprCnt = calcProgram.getExprCount
+
+ // compute number of non-field access expressions (computations,
conditions, etc.)
+ // we only want to account for computations, not for simple
projections.
+ val exprCnt =
calcProgram.getExprList.asScala.toList.count(!_.isInstanceOf[RexInputRef])
--- End diff --
maybe we could also exclude RexLiteral as well.
> 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}}.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
