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From "Halsey, Stephen" <>
Subject RE: Leaking org.apache.lucene.index.* objects
Date Fri, 09 Feb 2007 14:32:54 GMT
Hi Otis,

Its funny, but I'm having a memory leak with Hibernate that I spent the
whole of yesterday banging my head against a wall about and so when
searching for emails with Leak in the title came across your message.
I'm probably going to hit the same problem as you for long running
multi-threaded lucene index updates so am very interested in this.  I
found the only way to isolate the problem with Hibernate (and hence
prove it is a Hibernate-only problem) is to write a very simple test
program that recreates the problem.  Have you got a program that
recreates this, perhaps one that creates two simple indexes, creates two
threads and slams away until it runs out of memory and every loop prints
the memory using this function:-

	private static long print_mem(long last_mem_free) {
		long mem_total = Runtime.getRuntime().totalMemory();
		long mem_free = Runtime.getRuntime().freeMemory();
		long mem_used = mem_total - mem_free;
		long mem_max = Runtime.getRuntime().maxMemory();
		long change = (mem_free - last_mem_free);

		LOG.debug((new Date()).toString() + " mem_free= " +
				+ " mem_total=" + mem_total
				+ " change=" + change
				+ " mem_used=" + mem_used
				+ " mem_max=" + mem_max);

		return mem_free;

The trick is to make the program very fast at accumalating memory, so
you can make it run out of memory quickly and also setting java args to
-Xms10m -Xmx10m or as low as you can and have it run for a minute so
that the JVM has to quickly try and reclaim memory.  This proves that
the JVM really can't free up memory, because the JVM will accumalate
memory whenever it feels like it, and sometimes only clear up when it
feels like it.

If you can send/write this test program and post it on the forum, I'll
give it a run and try using a copy of Jprofiler I have to locate the
objects that are accumalating memory (if I can work out how to use it

Just noticed this is from December, so may well be a bit late for
helping out?




>-----Original Message-----
>From: Otis Gospodnetic [] 
>Sent: 15 December 2006 17:28
>Subject: Leaking org.apache.lucene.index.* objects
>About 2-3 weeks ago I emailed about a memory leak in my 
>application.  I then found some problems in my code (I wasn't 
>closing IndexSearchers explicitly) and took care of those.  
>Now I see my app is still leaking memory - jconsole clearly 
>shows the "Tenured Gen" memory pool getting filled up until I 
>hit the OOM, but I can't seem to pin-point the source.
>I found that a bunch or o.a.l.index.* objects are not getting 
>GCed, even though they should.  For example:
>$ jmap -histo:live 7825 | grep apache.lucene.index | head -20 
>| sort -k2 -nr
>num   #instances    #bytes  class name
>  4:   1764840    98831040  
>  5:   2119215    67814880  org.apache.lucene.index.TermInfo
>  7:   1112459    35598688  org.apache.lucene.index.SegmentReader$Norm
>  9:   2132311    34116976  org.apache.lucene.index.Term
> 12:   1117897    26829528  org.apache.lucene.index.FieldInfo
> 13:    225340    18027200  org.apache.lucene.index.SegmentTermEnum
> 15:    589727    14153448  org.apache.lucene.index.TermBuffer
> 21:     86033     8718504  [Lorg.apache.lucene.index.TermInfo;
> 20:     86033     8718504  [Lorg.apache.lucene.index.Term;
> 23:     86120     7578560  org.apache.lucene.index.SegmentReader
> 26:     90501     5068056
> 27:     86120     4822720  org.apache.lucene.index.TermInfosReader
> 33:     86130     3445200  org.apache.lucene.index.SegmentInfo
> 36:     87355     2795360  
> 38:     86120     2755840  org.apache.lucene.index.FieldsReader
> 39:     86050     2753600  org.apache.lucene.index.CompoundFileReader
> 42:     46903     2251344  org.apache.lucene.index.SegmentInfos
> 43:     93778     2250672  
> 45:     93778     1500448  
> 47:     86510     1384160  org.apache.lucene.index.FieldInfos
>I'm running my app in search-only mode - no adds or deletes.
>The counts of these objects just keeps going up, even though I 
>am explicitly closing the IndexSearcher.  I can see that file 
>descriptors _are_ freed up after searcher.close(), because 
>lsof no longer shows them, but the above objects just linger 
>and accumulate, even when I force GC via jconsole or via the profiler.
>I thought maybe various *Readers are not getting close()d, but 
>I've double-checked all *Readers above, and they all seem to 
>close their IndexInput references.  The static nested class 
>CompoundFileReader.CSIndexInput has a close() without any 
>implementation.  At first I thought that was an omission, but 
>adding a close of the inner IndexInput there resulted in a 
>search-time error.  I've added the lovely print debugging to 
>various close() methods and see those methods being called.  
>I've added finalize() with some print debugging to 
>SegmentReader, TermInfosReader, SegmentTermEnum, FieldsReader, 
>and CompoundFileReader.  All but CFReader get finalized after a while.
>My application is running as a webapp and has thousands of 
>separate indices.  This means it's very multi-threaded and the 
>servlet container has a pool of threads that handle requests, 
>and each request may be for a different index.  I cache 
>IndexSearchers for a while, and purge/close them every N 
>minutes if they have been idle more than M minutes.
>It occurred to me last night that things like TermInfosReader 
>and SegmentReader are using ThreadLocal, and since threads are 
>used in a thread pool, and thus shared with requests handling 
>searches against different indices, it's not clear to me what 
>happens with object instances that are put in those 
>ThreadLocals in such scenario.  Aren't things going to step on 
>each others' toes?
>TIR has close() and SR has doClose(), so I put <TL 
>inst>.set(null) there.  This immediately got rid of those 
>instances of CompoundFileReader.CSIndexInput in my dev 
>environment!!!! Yeeees!
>But in my dev environment I tested my additions by slamming my 
>app against a *single* index.  I took my modified Lucene to 
>production, and quickly saw all those o.a.l.index.* objects 
>accumulate again.  I also see a lot of ThreadLocal's kids:
> 16:    419387    13420384  java.lang.ThreadLocal$ThreadLocalMap$Entry
>I *think* that points out to some issues with how that 
>ThreadLocal is used there, in a multi-threaded, multi-index 
>I'm running JDK 6, and while this problem sounds a bit like 
>LUCENE-436, I'm not yet sure if it's the same thing.  
>Because my IndexSearchers (and thus all those o.a.l.index.* 
>objects) are long-lived, and threads are shared and reused for 
>searching of other indices, those close() and doClose() 
>methods are not called at the end of the request life-cycle, 
>so at the end of the request those TL instances will *still* 
>have something in them.  When their thread is later reused for 
>searching of another index, new data will be put in them, but 
>the old data will never be cleaned out!  No?
>It seems a bit odd, but with this ThreadLocals, shouldn't a 
>multi-threaded, multi-index webapp really have to "clean" 
>those ThreadLocal instances either before or at the end of the request?
>I'm running out of ideas, and was wondering if anyone has any 
>thoughts about what could still be holding references to the 
>above classes.  I have some 20-30MB memory snapshots (via 
>YourKit) and heap dumps (via jmap), if anyone is interested.
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