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https://issues.apache.org/jira/browse/MAPREDUCE-1372?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Amar Kamat updated MAPREDUCE-1372:
----------------------------------
Attachment: ReadOnly.java
I tested the use of Collections.newSetFromMap with the testcase attached and
here are the results
Pre patch
||num items||avg time to scan in ms||
|1000|0|
|10000|9|
|100000|13|
|1000000|56|
|10000000|424|
Post patch
||num items||avg time to scan in ms||
|1000|0|
|10000|7|
|100000|21|
|1000000|124|
|10000000|1175|
Using the command
{code}
java ReadOnly -correctness pre|post
{code}
the bug can be verified. The bug can be reproduced by using the _pre_ switch
and the fix can be verified by switching to _post_. With _pre_, a HashMap is
used while with _post_ a Collections.newSetFromMap is used. The test is simple.
It simply starts 2 threads, one adding to the set while the other scans it.
Using the command
{code}
java ReadOnly -performance pre|post X Y
{code}
the proposed change can be benchmarked. The benchmark simply adds to a set
(determined by pre/post switch) X elements and scanning it Y times, averaging
it over runs.
> ConcurrentModificationException in JobInProgress
> ------------------------------------------------
>
> Key: MAPREDUCE-1372
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-1372
> Project: Hadoop Map/Reduce
> Issue Type: Bug
> Components: jobtracker
> Affects Versions: 0.20.1
> Reporter: Amareshwari Sriramadasu
> Priority: Blocker
> Fix For: 0.21.0
>
> Attachments: M1372-0.patch, M1372-1.patch, M1372-2.patch,
> ReadOnly.java
>
>
> We have seen the following ConcurrentModificationException in one of our
> clusters
> {noformat}
> java.io.IOException: java.util.ConcurrentModificationException
> at java.util.HashMap$HashIterator.nextEntry(HashMap.java:793)
> at java.util.HashMap$KeyIterator.next(HashMap.java:828)
> at
> org.apache.hadoop.mapred.JobInProgress.findNewMapTask(JobInProgress.java:2018)
> at
> org.apache.hadoop.mapred.JobInProgress.obtainNewMapTask(JobInProgress.java:1077)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$MapSchedulingMgr.obtainNewTask(CapacityTaskScheduler.java:796)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.getTaskFromQueue(CapacityTaskScheduler.java:589)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.assignTasks(CapacityTaskScheduler.java:677)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler$TaskSchedulingMgr.access$500(CapacityTaskScheduler.java:348)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler.addMapTask(CapacityTaskScheduler.java:1397)
> at
> org.apache.hadoop.mapred.CapacityTaskScheduler.assignTasks(CapacityTaskScheduler.java:1349)
> at org.apache.hadoop.mapred.JobTracker.heartbeat(JobTracker.java:2976)
> at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
> at
> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> at java.lang.reflect.Method.invoke(Method.java:597)
> at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:508)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:959)
> at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:955)
> at java.security.AccessController.doPrivileged(Native Method)
> at javax.security.auth.Subject.doAs(Subject.java:396)
> at org.apache.hadoop.ipc.Server$Handler.run(Server.java:953)
> {noformat}
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