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From "Nathan Roberts (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-4499) Looking for speculative tasks is very expensive in 1.x
Date Mon, 20 Aug 2012 22:02:38 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-4499?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13438259#comment-13438259
] 

Nathan Roberts commented on MAPREDUCE-4499:
-------------------------------------------

Ideally we'd be much less aggressive about calling findSpeculativeTask() (2 million calls
over a few seconds is a bit much).  However, this patch looks to be a safe way to mitigate
the problem by avoiding the seemingly expensive call to hasRunOnMachine(). I double checked
the truth table against the pseudo-code and the patch and they look good to me. 
                
> Looking for speculative tasks is very expensive in 1.x
> ------------------------------------------------------
>
>                 Key: MAPREDUCE-4499
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-4499
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: mrv1, performance
>    Affects Versions: 1.0.3
>            Reporter: Nathan Roberts
>         Attachments: mapreduce-4499-v1.0.2-1.patch
>
>
> When there are lots of jobs and tasks active in a cluster, the process of figuring out
whether or not to launch a speculative task becomes very expensive. 
> I could be missing something but it certainly looks like on every heartbeat we could
be scanning 10's of thousands of tasks looking for something which might need to be speculatively
executed. In most cases, nothing gets chosen so we completely trashed our data cache and didn't
even find a task to schedule, just to do it all over again on the next heartbeat.
> On busy jobtrackers, the following backtrace is very common:
> "IPC Server handler 32 on 50300" daemon prio=10 tid=0x00002ab36c74f800
> nid=0xb50 runnable [0x0000000045adb000]
>    java.lang.Thread.State: RUNNABLE
>         at java.util.TreeMap.valEquals(TreeMap.java:1182)
>         at java.util.TreeMap.containsValue(TreeMap.java:227)
>         at java.util.TreeMap$Values.contains(TreeMap.java:940)
>         at
> org.apache.hadoop.mapred.TaskInProgress.hasRunOnMachine(TaskInProgress.java:1072)
>         at
> org.apache.hadoop.mapred.JobInProgress.findSpeculativeTask(JobInProgress.java:2193)
>         - locked <0x00002aaefde82338> (a
> org.apache.hadoop.mapred.JobInProgress)
>         at
> org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:2417)
>         - locked <0x00002aaefde82338> (a
> org.apache.hadoop.mapred.JobInProgress)
>         at
> org.apache.hadoop.mapred.JobInProgress.obtainNewNonLocalMapTask(JobInProgress.java:1432)
>         - locked <0x00002aaefde82338> (a
> org.apache.hadoop.mapred.JobInProgress)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler$MapSchedulingMgr.obtainNewTask(CapacityTaskScheduler.java:525)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.getTaskFromQueue(CapacityTaskScheduler.java:322)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.assignTasks(CapacityTaskScheduler.java:419)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.access$500(CapacityTaskScheduler.java:150)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler.addMapTasks(CapacityTaskScheduler.java:1075)
>         at
> org.apache.hadoop.mapred.CapacityTaskScheduler.assignTasks(CapacityTaskScheduler.java:1044)
>         - locked <0x00002aab6e27a4c8> (a
> org.apache.hadoop.mapred.CapacityTaskScheduler)
>         at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:3398)
>         - locked <0x00002aab6e191278> (a org.apache.hadoop.mapred.JobTracker)
> ...

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