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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