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https://issues.apache.org/jira/browse/KAFKA-10871?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17253173#comment-17253173
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Matthias J. Sax commented on KAFKA-10871:
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I don't think this is a bug, but rather a performance optimization: We pass in
the `wallClockTime` parameter, to avoid calling `Time.milliseconds()` (that
translates to `System.currentTimeMillis()`) too often, because getting the
current time is a somewhat expensive call to make. The caller, ie, the
TaskManager calls `Time.milliseconds()` right before it calls `process()` and
thus we can save one expensive call to get the time by passing the the
wallClockTime.
> StreamTask shouldn't take WallClockTime as input parameter in process method
> ----------------------------------------------------------------------------
>
> Key: KAFKA-10871
> URL: https://issues.apache.org/jira/browse/KAFKA-10871
> Project: Kafka
> Issue Type: Bug
> Components: streams
> Affects Versions: 2.7.0
> Reporter: Rohit Deshpande
> Assignee: Rohit Deshpande
> Priority: Major
> Labels: newbie
>
> While working on https://issues.apache.org/jira/browse/KAFKA-10062 I realized
> process method in StreamTask is taking
> wallClockTime as input parameter which is redundant as StreamTask already
> contains
> time(https://github.com/apache/kafka/blob/2.5.0/streams/src/main/java/org/apache/kafka/streams/processor/internals/StreamTask.java#L75)
> field which represents wallClockTime.
> In process method
> (https://github.com/apache/kafka/blob/2.7/streams/src/main/java/org/apache/kafka/streams/processor/internals/StreamTask.java#L664),
> wallClockTime can be passed from StreamTask's time field itself.
> This method was changed as part of pr:
> https://github.com/apache/kafka/pull/7997.
> As part of https://issues.apache.org/jira/browse/KAFKA-10062, I believe
> wallClockTime need not be stored in
> ProcessorContext(https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/processor/internals/AbstractProcessorContext.java#L48)
> but should be fetched from StreamTask's time field. Reference pr:
> https://github.com/apache/kafka/pull/9744
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