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https://issues.apache.org/jira/browse/MAPREDUCE-6436?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15058917#comment-15058917
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zhihai xu commented on MAPREDUCE-6436:
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Thanks for the finding [~aw], Just know we branched out 2.8. Will commit it to
branch-2.8 shortly.
> JobHistory cache issue
> ----------------------
>
> Key: MAPREDUCE-6436
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-6436
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Reporter: Ryu Kobayashi
> Assignee: Kai Sasaki
> Priority: Blocker
> Fix For: 2.8.0, 2.7.3, 2.6.4
>
> Attachments: MAPREDUCE-6436.1.patch, MAPREDUCE-6436.2.patch,
> MAPREDUCE-6436.3.patch, MAPREDUCE-6436.4.patch, stacktrace1.txt,
> stacktrace2.txt, stacktrace3.txt
>
>
> Problem:
> HistoryFileManager.addIfAbsent produces large amount of logs if number of
> cached entries whose age is less than mapreduce.jobhistory.max-age-ms becomes
> larger than mapreduce.jobhistory.joblist.cache.size by far.
> Example:
> For example, if the cache contains 50000 entries in total and 10,000 entries
> newer than mapreduce.jobhistory.max-age-ms where
> mapreduce.jobhistory.joblist.cache.size is 20000,
> HistoryFileManager.addIfAbsent
> method produces 50000 - 20000 = 30000 lines of "Waiting to remove <key> from
> JobListCache because it is not in done yet" message.
> It will attach a stacktrace.
> Impact:
> In addition to large disk consumption, this issue blocks JobHistory.getJob
> long time and slows job execution down significantly because getJob is called
> by RPC such as HistoryClientService.HSClientProtocolHandler.getJobReport.
> This impact happens because HistoryFileManager.UserLogDir.scanIfNeeded
> eventually calls HistoryFileManager.addIfAbsent in a synchronized block. When
> multiple threads call scanIfNeeded simultaneously, one of them acquires lock
> and the other threads are blocked until the first thread completes
> long-running
> HistoryFileManager.addIfAbsent call.
> Solution:
> * Reduce amount of logs so that HistoryFileManager.addIfAbsent doesn't take
> too long time.
> * Good to have if possible: HistoryFileManager.UserLogDir.scanIfNeeded skips
> scanning if another thread is already scanning. This changes semantics of
> some HistoryFileManager methods (such as getAllFileInfo and getFileInfo)
> because scanIfNeeded keep outdated state.
> * Good to have if possible: Make scanIfNeeded asynchronous so that RPC calls
> are
> not blocked by a loop at scale of tens of thousands.
>
> This patch implemented the first item.
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