[jira] [Commented] (LUCENE-7570) Tragic events during merges can lead to deadlock

["ASF subversion and git services (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-7570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15736693#comment-15736693 ] 

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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