[jira] [Assigned] (FLINK-30533) IteratorSourceReaderBase#pollNext() should push records to ReaderOutput in a while loop

["Dong Lin (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/FLINK-30533?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Dong Lin reassigned FLINK-30533:
--------------------------------

    Assignee: Dong Lin

> IteratorSourceReaderBase#pollNext() should push records to ReaderOutput in a while loop
> ---------------------------------------------------------------------------------------
>
>                 Key: FLINK-30533
>                 URL: https://issues.apache.org/jira/browse/FLINK-30533
>             Project: Flink
>          Issue Type: Sub-task
>            Reporter: Dong Lin
>            Assignee: Dong Lin
>            Priority: Major
>
> Currently, each invocation of IteratorSourceReaderBase#pollNext() push at most one record to the given ReaderOutput. This unnecessarily increases the average Java call stack depth needed to produce an element.
>  
> Take the following program as an example. For each element produced by this program, Flink runtime needs to include in the call stack these 4 function calls:
>  * StreamTask#processInput()
>  * StreamOneInputProcessor#processInput()
>  * StreamTaskSourceInput#emitNext()
>  * SourceOperator#emitNext()
> {code:java}
> DataStream<Long> stream = env.fromSequence(1, 1000000000L)
> .map(x -> x)
> .addSink(new DiscardingSink<>());
> {code}
>  
> In comparison, SourceReaderBase#pollNext() is already using a while loop so that each invocation of this method could push as many records to the given ReaderOutput as possible.
>  
> This ticket proposes to update IteratorSourceReaderBase#pollNext() to push records to ReaderOutput in a while loop, for the following two reason:
>  * It improves performance for programs that IteratorSourceReaderBase (e.g. env.fromSequence) by removing an average of 4 function from the call stack needed to produce a record.
>  * It makes the behavior of IteratorSourceReaderBase and SourceReaderBase consistent with each other.



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