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https://issues.apache.org/jira/browse/BEAM-7520?focusedWorklogId=298955&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-298955
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ASF GitHub Bot logged work on BEAM-7520:
----------------------------------------

                Author: ASF GitHub Bot
            Created on: 21/Aug/19 19:56
            Start Date: 21/Aug/19 19:56
    Worklog Time Spent: 10m 
      Work Description: je-ik commented on pull request #9190: [BEAM-7520] Fix 
timer firing order in DirectRunner
URL: https://github.com/apache/beam/pull/9190#discussion_r316373884
 
 

 ##########
 File path: 
runners/direct-java/src/main/java/org/apache/beam/runners/direct/CommittedResult.java
 ##########
 @@ -18,10 +18,10 @@
 package org.apache.beam.runners.direct;
 
 import com.google.auto.value.AutoValue;
+import java.util.Optional;
 
 Review comment:
   Yes, I also think that the performance impact of creating one short lived 
instance should be negligible. I actually tried to measure it, but I didn't get 
any statistically significant difference in this case. Although, I have seen 
significant impact in other cases (getting rid of creating useless instance in 
one place of spark runner gave me about 20% performance gain, but that could 
have been very specific case). But that is probably not that significant to 
this PR. :-)
   
   To conclude this, I will drop the commit where I changed the Optional in 
DirectRunner and start a discuss thread related to making the usage consistent 
across the code base. Currently there is approx 3:2 usage of java.util vs. 
guava.
 
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Issue Time Tracking
-------------------

    Worklog Id:     (was: 298955)
    Time Spent: 8.5h  (was: 8h 20m)

> DirectRunner timers are not strictly time ordered
> -------------------------------------------------
>
>                 Key: BEAM-7520
>                 URL: https://issues.apache.org/jira/browse/BEAM-7520
>             Project: Beam
>          Issue Type: Bug
>          Components: runner-direct
>    Affects Versions: 2.13.0
>            Reporter: Jan Lukavský
>            Assignee: Jan Lukavský
>            Priority: Major
>          Time Spent: 8.5h
>  Remaining Estimate: 0h
>
> Let's suppose we have the following situation:
>  - statful ParDo with two timers - timerA and timerB
>  - timerA is set for window.maxTimestamp() + 1
>  - timerB is set anywhere between <windowStart, windowEnd), let's denote that 
> timerB.timestamp
>  - input watermark moves to BoundedWindow.TIMESTAMP_MAX_VALUE
> Then the order of timers is as follows (correct):
>  - timerB
>  - timerA
> But, if timerB sets another timer (say for timerB.timestamp + 1), then the 
> order of timers will be:
>  - timerB (timerB.timestamp)
>  - timerA (BoundedWindow.TIMESTAMP_MAX_VALUE)
>  - timerB (timerB.timestamp + 1)
> Which is not ordered by timestamp. The reason for this is that when the input 
> watermark update is evaluated, the WatermarkManager,extractFiredTimers() will 
> produce both timerA and timerB. That would be correct, but when timerB sets 
> another timer, that breaks this.



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