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From "Michael McCandless (JIRA)" <j...@apache.org>
Subject [jira] Created: (LUCENE-1638) Thread safety issue can cause index corruption when autoCommit=true and multiple threads are committing
Date Fri, 15 May 2009 17:31:45 GMT
Thread safety issue can cause index corruption when autoCommit=true and multiple threads are
committing
-------------------------------------------------------------------------------------------------------

                 Key: LUCENE-1638
                 URL: https://issues.apache.org/jira/browse/LUCENE-1638
             Project: Lucene - Java
          Issue Type: Bug
          Components: Index
    Affects Versions: 2.9
            Reporter: Michael McCandless
            Assignee: Michael McCandless
             Fix For: 2.9


This is only present in 2.9 trunk, but has been there since
LUCENE-1516 was committed I believe.

It's rare to hit: it only happens if multiple calls to commit() are in
flight (from different threads) and where at least one of those calls
is due to a merge calling commit (because autoCommit is true).

When it strikes, it leaves the index corrupt because it incorrectly
removes an active segment.  It causes exceptions like this:
{code}
java.io.FileNotFoundException: _1e.fnm
	at org.apache.lucene.store.MockRAMDirectory.openInput(MockRAMDirectory.java:246)
	at org.apache.lucene.index.FieldInfos.<init>(FieldInfos.java:67)
	at org.apache.lucene.index.SegmentReader.initialize(SegmentReader.java:536)
	at org.apache.lucene.index.SegmentReader.get(SegmentReader.java:468)
	at org.apache.lucene.index.SegmentReader.get(SegmentReader.java:414)
	at org.apache.lucene.index.IndexWriter$ReaderPool.get(IndexWriter.java:641)
	at org.apache.lucene.index.IndexWriter$ReaderPool.get(IndexWriter.java:627)
	at org.apache.lucene.index.DocumentsWriter.applyDeletes(DocumentsWriter.java:923)
	at org.apache.lucene.index.IndexWriter.applyDeletes(IndexWriter.java:4987)
	at org.apache.lucene.index.IndexWriter.doFlushInternal(IndexWriter.java:4165)
	at org.apache.lucene.index.IndexWriter.doFlush(IndexWriter.java:4025)
	at org.apache.lucene.index.IndexWriter.flush(IndexWriter.java:4016)
	at org.apache.lucene.index.IndexWriter.closeInternal(IndexWriter.java:2077)
	at org.apache.lucene.index.IndexWriter.close(IndexWriter.java:2040)
	at org.apache.lucene.index.IndexWriter.close(IndexWriter.java:2004)
	at org.apache.lucene.index.TestStressIndexing2.indexRandom(TestStressIndexing2.java:210)
	at org.apache.lucene.index.TestStressIndexing2.testMultiConfig(TestStressIndexing2.java:104)
{code}

It's caused by failing to increment changeCount inside the same
synchronized block where segmentInfos was changed, in commitMerge.
The fix is simple -- I plan to commit shortly.


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