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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MAPREDUCE-6797) Job history server scans can become blocked on a single, slow entry
Date Fri, 21 Oct 2016 05:51:58 GMT

    [ https://issues.apache.org/jira/browse/MAPREDUCE-6797?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15594162#comment-15594162
] 

Karthik Kambatla commented on MAPREDUCE-6797:
---------------------------------------------

If multiple threads call {{addIfAbsent}} simultaneously, is it possible they process the same
{{HistoryFileInfo}}? How do we ensure only one thread is processing a file? 

> Job history server scans can become blocked on a single, slow entry
> -------------------------------------------------------------------
>
>                 Key: MAPREDUCE-6797
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-6797
>             Project: Hadoop Map/Reduce
>          Issue Type: Bug
>          Components: jobhistoryserver
>    Affects Versions: 2.4.0, 2.8.0
>            Reporter: Prabhu Joseph
>            Assignee: Prabhu Joseph
>            Priority: Critical
>         Attachments: jstack
>
>
> There is one more piece of code in HistoryFileManager where Synchronized keyword on HistoryFileInfo
need to be removed. The JobHistoryServer contention issue is hit on our environment where
stacktrace (attached) shows the HistoryFileManager$JobListCache.addIfAbsent unnecessarily
waiting to lock on HistoryFileInfo.
> Synchronized on isMovePending and didMoveFail has been removed by Mapreduce-6684.
> {code}
> HistoryFileInfo firstValue = cache.get(key);
>     synchronized(firstValue) {  ---------------> Synchronized is not needed here
>               if (firstValue.isMovePending()) {
>                 if(firstValue.didMoveFail() && 
>                     firstValue.jobIndexInfo.getFinishTime() <= cutoff) {
>                   cache.remove(key);
>                   //Now lets try to delete it
>                   try {
>                     firstValue.delete();
>                   } catch (IOException e) {
>                     LOG.error("Error while trying to delete history files" +
>                     " that could not be moved to done.", e);
>                   }
>                 } else {
>                   LOG.warn("Waiting to remove " + key
>                       + " from JobListCache because it is not in done yet.");
>                 }
>               } else {
>                 cache.remove(key);
>               }
>             }
> {code}
> {code}
> Note: stacktrace is from hadoop-2.4.0 version and the problem exists in latest hadoop
as well
> "2144820863@qtp-313351300-38156" daemon prio=10 tid=0x0000000001e13800 nid=0xf133 waiting
for monitor entry [0x00007f7c1d8dd000]
>    java.lang.Thread.State: BLOCKED (on object monitor)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager$JobListCache.addIfAbsent(HistoryFileManager.java:226)
>         - waiting to lock <0x000000040145c4d8> (a org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager$HistoryFileInfo)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.scanIntermediateDirectory(HistoryFileManager.java:825)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.access$200(HistoryFileManager.java:82)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager$UserLogDir.scanIfNeeded(HistoryFileManager.java:280)
>         - locked <0x0000000400375388> (a org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager$UserLogDir)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.scanIntermediateDirectory(HistoryFileManager.java:792)
>         at org.apache.hadoop.mapreduce.v2.hs.HistoryFileManager.getAllFileInfo(HistoryFileManager.java:920)
>         at org.apache.hadoop.mapreduce.v2.hs.CachedHistoryStorage.getAllPartialJobs(CachedHistoryStorage.java:156)
>         at org.apache.hadoop.mapreduce.v2.hs.JobHistory.getAllJobs(JobHistory.java:235)
> {code}



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