[MAPREDUCE-4499] Looking for speculative tasks is very expensive in 1.x

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.0.3
• Fix Version/s: 1.2.0
• Component/s: mrv1, performance
• Target Version/s: 1.2.0
• Assignee: Koji Noguchi
• Reporter: Nathan Roberts
• Created: 31/Jul/12 21:50
• Updated: 15/May/13 05:15
• Resolved: 29/Aug/12 15:48

Description

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)
  ...)

Issue Links

• is related to: MAPREDUCE-1684 ClusterStatus can be cached in CapacityTaskScheduler.assignTasks()