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Posted to dev@lucene.apache.org by "Uwe Schindler (JIRA)" <ji...@apache.org> on 2013/04/13 11:40:16 UTC
[jira] [Resolved] (LUCENE-4930) Lucene's use of WeakHashMap at
index time prevents full use of cores on some multi-core machines, due to
contention
[ https://issues.apache.org/jira/browse/LUCENE-4930?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Uwe Schindler resolved LUCENE-4930.
-----------------------------------
Resolution: Fixed
Committed to 4.x and trunk!
Thansk Christian for the tip and to Karl for reporting the issue.
In any case, I would strongly recommend to report the bug to Ubuntu/IcedTea developers, because their OpenJDK6 variant contains has a bug fixed since Java 6u15.
Please note: This bug may be fixed for you while indexing, but e.g. FieldCache uses the default WeakHashMap in Lucene, so whenever some code retrives a field from the FieldCache, you have the sync bottleneck (but there is already other synchronization involved, so it may not be an issue at all). If you are using MMapDirectory with this broken JDK: On searching you may also get the same synchronization issue, because ByteBufferIndexInput relies on the WeakIdentityMap#put() operation (and really needs the cleanup, disabling reap() for puts would kill you JVM after a short time). Every search request that opens a TermsEnum, posting list,... will be affected. This is just a warning!
> Lucene's use of WeakHashMap at index time prevents full use of cores on some multi-core machines, due to contention
> -------------------------------------------------------------------------------------------------------------------
>
> Key: LUCENE-4930
> URL: https://issues.apache.org/jira/browse/LUCENE-4930
> Project: Lucene - Core
> Issue Type: Improvement
> Components: core/index
> Affects Versions: 4.2
> Environment: Dell blade system with 16 cores
> Reporter: Karl Wright
> Assignee: Uwe Schindler
> Fix For: 5.0, 4.3
>
> Attachments: LUCENE-4930.patch, LUCENE-4930.patch, LUCENE-4930.patch, LUCENE-4930.patch, thread_dump.txt
>
>
> Our project is not optimally using full processing power during under indexing load on Lucene 4.2.0. The reason is the AttributeSource.addAttribute() method, which goes through a WeakHashMap synchronizer, which is apparently single-threaded for a significant amount of time. Have a look at the following trace:
> "pool-1-thread-28" prio=10 tid=0x00007f47fc104800 nid=0x672b waiting for monitor entry [0x00007f47d19ed000]
> java.lang.Thread.State: BLOCKED (on object monitor)
> at java.lang.ref.ReferenceQueue.poll(ReferenceQueue.java:98)
> - waiting to lock <0x00000005c5cd9988> (a java.lang.ref.ReferenceQueue$Lock)
> at org.apache.lucene.util.WeakIdentityMap.reap(WeakIdentityMap.java:189)
> at org.apache.lucene.util.WeakIdentityMap.get(WeakIdentityMap.java:82)
> at org.apache.lucene.util.AttributeSource$AttributeFactory$DefaultAttributeFactory.getClassForInterface(AttributeSource.java:74)
> at org.apache.lucene.util.AttributeSource$AttributeFactory$DefaultAttributeFactory.createAttributeInstance(AttributeSource.java:65)
> at org.apache.lucene.util.AttributeSource.addAttribute(AttributeSource.java:271)
> at org.apache.lucene.index.DocInverterPerField.processFields(DocInverterPerField.java:107)
> at org.apache.lucene.index.DocFieldProcessor.processDocument(DocFieldProcessor.java:254)
> at org.apache.lucene.index.DocumentsWriterPerThread.updateDocument(DocumentsWriterPerThread.java:256)
> at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:376)
> at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:1473)
> at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:1148)
> at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:1129)
> …
> We’ve had to make significant changes to the way we were indexing in order to not hit this issue as much, such as indexing using TokenStreams which we reuse, when it would have been more convenient to index with just tokens. (The reason is that Lucene internally creates TokenStream objects when you pass a token array to IndexableField, and doesn’t reuse them, and the addAttribute() causes massive contention as a result.) However, as you can see from the trace above, we’re still running into contention due to other addAttribute() method calls that are buried deep inside Lucene.
> I can see two ways forward. Either not use WeakHashMap or use it in a more efficient way, or make darned sure no addAttribute() calls are done in the main code indexing execution path. (I think it would be easy to fix DocInverterPerField in that way, FWIW. I just don’t know what we’ll run into next.)
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