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https://issues.apache.org/jira/browse/MAPREDUCE-5124?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16247740#comment-16247740
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Peter Bacsko commented on MAPREDUCE-5124:
-----------------------------------------
Just a quick update on the GC usage improvement. I know the POC is not the
final version, but I still, I decided to check how much it improves.
I added a 2 second sleep to {{StatusUpdater.transition()}} to cause event
backlog and used a mapper code which constantly called {{reporter.progress()}}
in a loop. I also decreased update interval to 100 ms.
GC events in the with the old code:
{noformat}
[GC (Allocation Failure) 52224K->8221K(200192K), 0.0130368 secs]
[GC (Allocation Failure) 60445K->10200K(252416K), 0.0119459 secs]
[GC (Metadata GC Threshold) 59477K->10902K(252416K), 0.0151800 secs]
[Full GC (Metadata GC Threshold) 10902K->9053K(201216K), 0.0446707 secs]
[GC (Allocation Failure) 113501K->19028K(251904K), 0.0136092 secs]
[GC (Metadata GC Threshold) 78026K->17595K(305664K), 0.0226579 secs]
[Full GC (Metadata GC Threshold) 17595K->12774K(347648K), 0.0501647 secs]
[GC (Allocation Failure) 221670K->24081K(377344K), 0.0199000 secs]
[GC (Allocation Failure) 260113K->29187K(378368K), 0.0277259 secs]
[GC (Allocation Failure) 265219K->39660K(373248K), 0.0384575 secs]
[GC (Allocation Failure) 267500K->48473K(378368K), 0.0370554 secs]
[GC (Allocation Failure) 276313K->55049K(371200K), 0.0417077 secs]
[GC (Allocation Failure) 275721K->61521K(365568K), 0.0270593 secs]
[GC (Allocation Failure) 275025K->67873K(359936K), 0.0417392 secs]
[GC (Allocation Failure) 274721K->74129K(345088K), 0.0531881 secs]
[GC (Allocation Failure) 274833K->80089K(347648K), 0.0270885 secs]
[GC (Allocation Failure) 274649K->85921K(345088K), 0.0313155 secs] <-- I
killed the job at this point
{noformat}
With the POC:
{noformat}
[GC (Allocation Failure) 52224K->8183K(200192K), 0.0228069 secs]
[GC (Allocation Failure) 60407K->10370K(252416K), 0.0135163 secs]
[GC (Metadata GC Threshold) 60383K->10958K(252416K), 0.0174618 secs]
[Full GC (Metadata GC Threshold) 10958K->8924K(198144K), 0.0452158 secs]
[GC (Allocation Failure) 113372K->18810K(254976K), 0.0132976 secs]
[GC (Metadata GC Threshold) 80801K->17577K(302592K), 0.0137089 secs]
[Full GC (Metadata GC Threshold) 17577K->12903K(345088K), 0.0579774 secs]
[GC (Allocation Failure) 221799K->24221K(382976K), 0.0188251 secs]
[GC (Allocation Failure) 268445K->24870K(384000K), 0.0164503 secs]
[GC (Allocation Failure) 269094K->19999K(381952K), 0.0155673 secs] <-- final
event
{noformat}
I think the difference speaks for itself.
> AM lacks flow control for task events
> -------------------------------------
>
> Key: MAPREDUCE-5124
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5124
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: mr-am
> Affects Versions: 2.0.3-alpha, 0.23.5
> Reporter: Jason Lowe
> Assignee: Peter Bacsko
> Attachments: MAPREDUCE-5124-CoalescingPOC-1.patch,
> MAPREDUCE-5124-CoalescingPOC2.patch, MAPREDUCE-5124-proto.2.txt,
> MAPREDUCE-5124-prototype.txt
>
>
> The AM does not have any flow control to limit the incoming rate of events
> from tasks. If the AM is unable to keep pace with the rate of incoming
> events for a sufficient period of time then it will eventually exhaust the
> heap and crash. MAPREDUCE-5043 addressed a major bottleneck for event
> processing, but the AM could still get behind if it's starved for CPU and/or
> handling a very large job with tens of thousands of active tasks.
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