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https://issues.apache.org/jira/browse/LUCENE-7570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15736693#comment-15736693
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ASF subversion and git services commented on LUCENE-7570:
---------------------------------------------------------
Commit 2b073a2f296289617bea8256d7efec06049df739 in lucene-solr's branch
refs/heads/master from Mike McCandless
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=2b073a2 ]
LUCENE-7570: don't run merges while holding the commitLock to prevent deadlock
when merges are stalled and a tragic merge exception strikes
> Tragic events during merges can lead to deadlock
> ------------------------------------------------
>
> Key: LUCENE-7570
> URL: https://issues.apache.org/jira/browse/LUCENE-7570
> Project: Lucene - Core
> Issue Type: Bug
> Components: core/index
> Affects Versions: 5.5, master (7.0)
> Reporter: Joey Echeverria
> Attachments: LUCENE-7570.patch, thread_dump.txt
>
>
> When an {{IndexWriter#commit()}} is stalled due to too many pending merges,
> you can get a deadlock if the currently active merge thread hits a tragic
> event.
> # The thread performing the commit synchronizes on the the {{commitLock}} in
> {{commitInternal}}.
> # The thread goes on to to call {{ConcurrentMergeScheduler#doStall()}} which
> {{waits()}} on the {{ConcurrentMergeScheduler}} object. This release the
> merge scheduler's monitor lock, but not the {{commitLock}} in {{IndexWriter}}.
> # Sometime after this wait begins, the merge thread gets a tragic exception
> can calls {{IndexWriter#tragicEvent()}} which in turn calls
> {{IndexWriter#rollbackInternal()}}.
> # The {{IndexWriter#rollbackInternal()}} synchronizes on the {{commitLock}}
> which is still held by the committing thread from (1) above which is waiting
> on the merge(s) to complete. Hence, deadlock.
> We hit this bug with Lucene 5.5, but I looked at the code in the master
> branch and it looks like the deadlock still exists there as well.
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