Nathan Roberts created MAPREDUCE-4499:
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Summary: 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
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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