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From Michael McCandless <>
Subject Re: IndexWriter and memory usage
Date Sat, 03 Apr 2010 09:38:49 GMT
Hmm why is the heap dump so immense?  Normally it contains the top N
(eg 100) object types and their count/aggregate RAM usage.

Can you attach the infoStream output to an email (to java-user)?


On Fri, Apr 2, 2010 at 5:28 PM, Woolf, Ross <> wrote:
> I have this and the heap dump is 63mb zipped.  The info stream is much smaller (31 kb
zipped), but I don't know how to get them to you.
> We are not using the NRT readers
> -----Original Message-----
> From: Michael McCandless []
> Sent: Thursday, April 01, 2010 5:21 PM
> To:
> Subject: Re: IndexWriter and memory usage
> Hmm, not good.  Can you post a heap dump?  Also, can you turn on
> infoStream, index up to the OOM @ 512 MB, and post the output?
> IndexWriter should not hang onto much beyond the RAM buffer.  But, it
> does allocate and then recycle this RAM buffer, so even in an idle
> state (having indexed enough docs to fill up the RAM buffer at least
> once) it'll hold onto those 16 MB.
> Are you using getReader (to get your NRT readers)?  If so, are you
> really sure you're eventually closing the previous reader after
> opening a new one?
> Mike
> On Thu, Apr 1, 2010 at 6:58 PM, Woolf, Ross <> wrote:
>> We are seeing a situation where the IndexWriter is using up the Java Heap space and
only releases memory for garbage collection upon a commit.   We are using the default RAMBufferSize
of 16 mb.  We are using Lucene 2.9.1. We are set at heap size of 512 mb.
>> We have a large number of documents that are run through Tika and then added to the
index.  The data from Tika is changed to a string, and then sent to Lucene.  Heap dumps
clearly show the data in the Lucene classes and not in Tika.  Our intent is to only perform
a commit once the entire indexing run is complete, but several hours into the process everything
comes to a crawl.  In using both JConsole and VisualVM  we can see that the heap space is
maxed out and garbage collection is not able to clean up any memory once we get into this
state.  It is our understanding that the IndexWriter should be only holding onto 16 mb of
data before it flushes it, but what we are seeing is that while it is in fact writing data
to disk when it hits the 16 mb limit, it is also holding onto some data in memory and not
allowing garbage collection to take place, and this continues until garbage collection is
unable to free up enough space to all things to move faster than a crawl.
>> As a test we caused a commit to occur after each document is indexed and we see the
total amount of memory reduced from nearly 100% of the Java Heap to around 70-75%.  The profiling
tools now show that the memory is cleaned up to some extent after each document.  But of
course this completely defeats the whole reason why we want to only commit at the end of the
run for performance sake.  Most of the data, as seen using Heap analasis, is held in Byte,
Character, and Integer classes whos GC roots are tied back to the Writer Objects and threads.
 The instance counts, after running just 1,100 documents seems staggering
>> Is there additional data that the IndexWriter hangs onto regardless of when it hits
the RAMBufferSize limit?  Why are we seeing the heap space all being used up?
>> A side question to this is the fact that we always see a large amount of memory used
by the IndexWriter even after our indexing has been completed and all commits have taken place
(basically in an idle state).  Why would this be?  Is the only way to totally clean up the
memory is to close the writer?  Our index is also used for real time indexing so the IndexWriter
is intended to remain open for the lifetime of the app.
>> Any help in understanding why the IndexWriter is maxing out our heap space or what
is expected from memory usage of the IndexWriter would be appreciated.
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