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https://issues.apache.org/jira/browse/BEAM-9308?focusedWorklogId=391021&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-391021
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ASF GitHub Bot logged work on BEAM-9308:
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Author: ASF GitHub Bot
Created on: 22/Feb/20 01:55
Start Date: 22/Feb/20 01:55
Worklog Time Spent: 10m
Work Description: reuvenlax commented on issue #10852: [BEAM-9308]
Decorrelate state cleanup timers
URL: https://github.com/apache/beam/pull/10852#issuecomment-589904689
As written, this is incorrect. We currently rely on the state cleanup timer
for watermark holds. This PR will cause that hold to be pushed later, which can
cause incorrect grouping for any downstream aggregations. This is something we
might be able to address by using the new outputTimestamp.
This requires some thought though. Delaying the timer will also prevent
downstream aggregations from firing. 3 minutes could cause issues if the
window itself is much smaller. We want to reuse this timer for
OnWindowExpiration, and this will delay all those callbacks as well.
I wonder if it would be better to first root cause why the GC timers caused
issues for your pipeline. One possibility: I believe that today any timers for
a key are always prioritized over any data for that key. Maybe we need a better
prioritization strategy so that large #s of timers don't starve out elements?
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Issue Time Tracking
-------------------
Worklog Id: (was: 391021)
Time Spent: 40m (was: 0.5h)
> Optimize state cleanup at end-of-window
> ---------------------------------------
>
> Key: BEAM-9308
> URL: https://issues.apache.org/jira/browse/BEAM-9308
> Project: Beam
> Issue Type: Improvement
> Components: runner-dataflow
> Reporter: Steve Niemitz
> Assignee: Steve Niemitz
> Priority: Major
> Time Spent: 40m
> Remaining Estimate: 0h
>
> When using state with a large keyspace, you can end up with a large amount of
> state cleanup timers set to fire all 1ms after the end of a window. This can
> cause a momentary (I've observed 1-3 minute) lag in processing while windmill
> and the java harness fire and process these cleanup timers.
> By spreading the firing over a short period after the end of the window, we
> can decorrelate the firing of the timers and smooth the load out, resulting
> in much less impact from state cleanup.
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