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From "ASF GitHub Bot (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-3849) Add FilterableTableSource interface and translation rule
Date Fri, 17 Mar 2017 08:34:41 GMT

    [ https://issues.apache.org/jira/browse/FLINK-3849?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15929583#comment-15929583
] 

ASF GitHub Bot commented on FLINK-3849:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/3520#discussion_r106603629
  
    --- Diff: flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/rules/common/PushFilterIntoTableSourceScanRuleBase.scala
---
    @@ -36,36 +43,34 @@ trait PushFilterIntoTableSourceScanRuleBase {
           filterableSource: FilterableTableSource[_],
           description: String): Unit = {
     
    -    if (filterableSource.isFilterPushedDown) {
    -      // The rule can get triggered again due to the transformed "scan => filter"
    -      // sequence created by the earlier execution of this rule when we could not
    -      // push all the conditions into the scan
    -      return
    -    }
    +    Preconditions.checkArgument(!filterableSource.isFilterPushedDown)
     
         val program = calc.getProgram
    +    val functionCatalog = FunctionCatalog.withBuiltIns
         val (predicates, unconvertedRexNodes) =
           RexProgramExtractor.extractConjunctiveConditions(
             program,
             call.builder().getRexBuilder,
    -        tableSourceTable.tableEnv.getFunctionCatalog)
    +        functionCatalog)
         if (predicates.isEmpty) {
           // no condition can be translated to expression
           return
         }
     
    -    val (newTableSource, remainingPredicates) = filterableSource.applyPredicate(predicates)
    -    // trying to apply filter push down, set the flag to true no matter whether
    -    // we actually push any filters down.
    -    newTableSource.setFilterPushedDown(true)
    +    val remainingPredicates = new util.LinkedList[Expression]()
    +    predicates.foreach(e => remainingPredicates.add(e))
    +
    +    val newTableSource = filterableSource.applyPredicate(remainingPredicates)
    --- End diff --
    
    That was actually one of the reasons for converting the predicate to CNF. In CNF you can
either evaluate a complete term or skip it and let a Calc evaluate it later. I don't see a
case where it would make sense to modify a conjunctive term but not evaluating it. Of course,
the table source could reorganize the expressions but what would be the purpose of that? IMO,
this could be error prone and introduce bugs.
    
    Do you have a concrete use case in mind, when a `FilterableTableSource` would modify the
expressions that it does not evaluate?


> Add FilterableTableSource interface and translation rule
> --------------------------------------------------------
>
>                 Key: FLINK-3849
>                 URL: https://issues.apache.org/jira/browse/FLINK-3849
>             Project: Flink
>          Issue Type: New Feature
>          Components: Table API & SQL
>            Reporter: Fabian Hueske
>            Assignee: Kurt Young
>
> Add a {{FilterableTableSource}} interface for {{TableSource}} implementations which support
filter push-down.
> The interface could look as follows
> {code}
> def trait FilterableTableSource {
>   // returns unsupported predicate expression
>   def setPredicate(predicate: Expression): Expression
> }
> {code}
> In addition we need Calcite rules to push a predicate (or parts of it) into a TableScan
that refers to a {{FilterableTableSource}}. We might need to tweak the cost model as well
to push the optimizer in the right direction.



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