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https://issues.apache.org/jira/browse/KAFKA-938?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13681479#comment-13681479
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Joel Koshy commented on KAFKA-938:
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Excellent catch Sam!
One comment: I think the DelayedItem class was intended to support arbitrary
(non-millisecond) timunits but that was buggy in two ways:
(i) The getDelay's 'unit' parameter shadowed the DelayedItem's 'unit' member
(ii) The delayMs val assumes that the delay is always in ms (which prevents
DelayedItem from supporting arbitrary time units).
Also, I think we must have missed the bit of the DelayQueue documentation that
says getDelay is called with TimeUnit.NANOSECONDS
I think we can tweak this a bit to make it support arbitrary timeunits -
otherwise, the "unit" parameter of DelayedItem is of no use. I can attach a
patch to make this clearer.
> High CPU usage when more or less idle
> -------------------------------------
>
> Key: KAFKA-938
> URL: https://issues.apache.org/jira/browse/KAFKA-938
> Project: Kafka
> Issue Type: Bug
> Components: core
> Affects Versions: 0.8
> Reporter: Sam Meder
> Priority: Critical
> Fix For: 0.8
>
> Attachments: timeunit.patch
>
>
> We've noticed Kafka using a lot of CPU in a pretty much idle environment and
> tracked it down to it's DelayedItem implementation. In particular, the time
> conversion for how much longer to wait:
> def getDelay(unit: TimeUnit): Long = {
> val elapsedMs = (SystemTime.milliseconds - createdMs)
> unit.convert(max(delayMs - elapsedMs, 0), unit)
> }
> does not actually convert, so Kafka ends up treating a ms value like
> nanoseconds, e.g. waking up every 100 ns or so. The above code should really
> be:
> def getDelay(unit: TimeUnit): Long = {
> val elapsedMs = (SystemTime.milliseconds - createdMs)
> unit.convert(max(delayMs - elapsedMs, 0), TimeUnit.MILLISECONDS)
> }
> I'll attach a patch.
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