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From "Simon Willnauer (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-3551) Yet another race in IW#nrtIsCurrent
Date Thu, 03 Nov 2011 13:05:32 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-3551?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Simon Willnauer updated LUCENE-3551:
------------------------------------

    Attachment: LUCENE-3551.patch

I isolated the problem in SOLR-2861 into a lucene testcase that fails reproduceable &
very very quickly. (passed on 3.x too though) 

with the fixes in this patch it passes reliably. The problem among the others I already explained
is that once DW has flushed all threads and put all deletes in the frozenPacketBuffer we have
a little window where those changes are not taken into account. This only happens if I only
flush deletes (no documents) since we prune the frozenBufferedDeletes before we checkpoint
so nrtIsCurrent doesn't see those changes for a little while. 
                
> Yet another race in IW#nrtIsCurrent
> -----------------------------------
>
>                 Key: LUCENE-3551
>                 URL: https://issues.apache.org/jira/browse/LUCENE-3551
>             Project: Lucene - Java
>          Issue Type: Bug
>          Components: core/index
>    Affects Versions: 4.0
>            Reporter: Simon Willnauer
>             Fix For: 4.0
>
>         Attachments: LUCENE-3551.patch, LUCENE-3551.patch, LUCENE-3551.patch, LUCENE-3551.patch
>
>
> In IW#nrtIsCurrent looks like this:
> {code}
>   synchronized boolean nrtIsCurrent(SegmentInfos infos) {
>     ensureOpen();
>     return infos.version == segmentInfos.version && !docWriter.anyChanges() &&
!bufferedDeletesStream.any();
>   }
> {code}
> * the version changes once we checkpoint the IW
> * docWriter has changes if there are any docs in ram or any deletes in the delQueue
> * bufferedDeletes contain all frozen del packages from the delQueue
> yet, what happens is 1. we decrement the numDocsInRam in DWPT#doAfterFlush (which is
executed during DWPT#flush) but before we checkpoint. 2. if we freeze deletes (empty the delQueue)
we put them in the flushQueue to maintain the order.  This means they are not yet in the bufferedDeleteStream.
> Bottom line, there is a window where we could see IW#nrtIsCurrent returning true if we
check within this particular window. Phew, I am not 100% sure if that is the reason for our
latest failure in SOLR-2861 but from what the logs look like this could be what happens. If
we randomly hit low values for maxBufferedDocs & maxBufferedDeleteTerms this is absolutely
possible.

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