[jira] Resolved: (LUCENE-1397) When BG merge hits an exception, optimize sometimes throws an IOException missing the root cause

["Michael McCandless (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/LUCENE-1397?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Michael McCandless resolved LUCENE-1397.
----------------------------------------

    Resolution: Fixed

Committed revision 698025 (trunk) and 698026 (2.4)

> When BG merge hits an exception, optimize sometimes throws an IOException missing the root cause
> ------------------------------------------------------------------------------------------------
>
>                 Key: LUCENE-1397
>                 URL: https://issues.apache.org/jira/browse/LUCENE-1397
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: Index
>    Affects Versions: 2.4
>            Reporter: Michael McCandless
>            Assignee: Michael McCandless
>            Priority: Minor
>             Fix For: 2.4, 2.9
>
>         Attachments: LUCENE-1397.patch
>
>
> When IndexWriter.optimize() is called, ConcurrentMergeScheduler will
> run the requested merges with background threads and optimize() will
> wait for these merges to complete.
> If a merge hits an exception, it records the root cause exception such
> that optimize can then retrieve this root cause and throw its own
> exception, with the root cause.
> But there is a bug: sometimes, the fact that an exception occurred on
> a merge is recorded, but the root cause is missing.  In this cause,
> optimize() still throws an exception (correctly indicating that the
> optimize() has not finished successfully), but it's not helpful
> because it's missing the root cause.  You must then go find the root
> cause in the JRE's stderr logs.
> This has hit a few users on this lists, most recently:
>   http://www.nabble.com/Background-merge-hit-exception-td19540409.html#a19540409
> I found the isssue, and finally got a unit test to intermittently show
> it.  It's a simple thread safety issue: in a finally clause in
> IndexWriter.merge we record the fact that the merge hit an exception
> before actually setting the root cause, and then only in
> ConcurrentMergeScheduler's exception handler do we set the root
> cause.  If the optimize thread is scheduled in between these two, it
> can throw an exception missing its root cause.
> The fix is straightforward.  I plan to commit to 2.4 & 2.9.

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