[LUCENE-6811] AnalyzingInfixSuggester cannot be used in more than one thread

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Affects Version/s: 5.3
• Component/s: modules/other
• Labels: suggester
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Lukhnos Liu
• Created: 22/Sep/15 05:14
• Updated: 28/Aug/22 14:43
• Resolved: 07/Mar/16 05:17

Description

Currently AnalyzingInfixSuggester always opens an index writer, even if the suggester will be used entirely in read-only mode. I was trying to serve suggestions out of the same index in a multithreaded setup, but I could only create one suggester per index per process because of this design.

I've created a GitHub project to demonstrate the bug: https://github.com/lukhnos/lucene-analyzing-infix-suggester-bug

To run the demo:

./gradlew build
java -jar build/libs/lucene-analyzing-infix-suggester-bug.jar

The exception reads:

Exception in thread "Thread-1" java.lang.RuntimeException: org.apache.lucene.store.LockObtainFailedException: Lock held by this virtual machine: <INDEX DIR>/write.lock
    at org.lukhnos.lucenestudy.AnalyzingInfixSuggesterBug$1SuggestReader.run(AnalyzingInfixSuggesterBug.java:65)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.lucene.store.LockObtainFailedException: Lock held by this virtual machine: <INDEX DIR>/write.lock
    at org.apache.lucene.store.NativeFSLockFactory.obtainFSLock(NativeFSLockFactory.java:127)
    at org.apache.lucene.store.FSLockFactory.obtainLock(FSLockFactory.java:41)
    at org.apache.lucene.store.BaseDirectory.obtainLock(BaseDirectory.java:45)
    at org.apache.lucene.index.IndexWriter.<init>(IndexWriter.java:775)
    at org.apache.lucene.search.suggest.analyzing.AnalyzingInfixSuggester.<init>(AnalyzingInfixSuggester.java:251)
    at org.apache.lucene.search.suggest.analyzing.AnalyzingInfixSuggester.<init>(AnalyzingInfixSuggester.java:163)
    at org.lukhnos.lucenestudy.AnalyzingInfixSuggesterBug$1SuggestReader.run(AnalyzingInfixSuggesterBug.java:51)
    ... 1 more

To work around this problem, I'm currently using my own modified "read only" AnalyzingInfixSuggester, in which I commented out the index writer creation code in the constructor. Then, in the lookup method, I also commented out the part where we get an EarlyTerminatingSortingCollector out of the index writer, so that only a TopFieldCollector is used.

I was wondering if a read-only mode can be added to AnalyzingInfixSuggester, or at least the contract of getIndexWriterConfig can be changed – since one will have to subclass to use a different index writer config anyway – such that if one returns null in getIndexWriterConfig, the suggester will operate in read-only mode, and so no index writer is created. Of course an error will have to be thrown if any build or update methods are called in such mode.