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From "Woolf, Ross" <Ross_Wo...@BMC.com>
Subject RE: IndexWriter and memory usage
Date Thu, 06 May 2010 17:03:04 GMT
Sorry to be so long in getting back on this. The patch you provided has improved the situation
but we are still seeing some memory loss.  The following are some images from the heap dump.
 I'll share with you what we are seeing now.

This first image shows the memory pattern.  Our fist commit takes place at about 3:54 when
the steady trend up takes a drop and the new cycle begins.   What we have found is the 2422
fix has made the memory in the first phase before the commit much better (and I'm sure throughout
the entire run).  But as you can see after the commit then we then again begin to lose memory.
 One of the pieces of info to know about this is what you are seeing, we have 5 threads that
are pushing data to our Lucene plugin.  If we drop it down to 1 thread then we are much more
successful and can actually index all of our data without running out of memory but at 5 threads
it gets into trouble.  We still see a trend up in memory usage, but not as severe as when
we use the multiple threads.
http://tinypic.com/view.php?pic=2w6bf68&s=5

There is another piece of the picture that I think might be coming into play.  We have plugged
Lucene into a legacy app and are subject to how we can get it to deliver the data that we
are indexing.  In some scenarios (like the one we are having this problem with) we are building
our documents progressively (adding fields to the document through the process).  What you
see before the first commit is the legacy system handing us the first field for many documents.
Once we have gotten all of "field 1" for all documents then we commit that data into the index.
 Then the system starts feeding us "field 2."  So we perform a search to see if the document
already exists (for the scenario you are seeing it does) and so it retrieves the original
document (we store a document ID) and it then adds the new field of data to the existing document
and we "update" the document in the index.  After the first commit, the rest of the process
is one where a document already exist and so the new field is added and and the document is
updated.  It is in this process that we start rapidly losing memory.  The following images
show some examples of common areas where memory is being held.

http://tinypic.com/view.php?pic=11vkwnb&s=5
http://tinypic.com/view.php?pic=abq9fp&s=5
http://tinypic.com/view.php?pic=25pskyp&s=5

As mentioned, we are subject to how we can have the legacy app feed us the data and so this
is why we do it this way.  We treat this system as a real time system and at anytime the legacy
system may send us a field that needs to be added or updated to a document.  So we search
for the document and if found we either add or update a field if the field is already existing
in the document.  So I started to wonder if a clue in this memory loss comes from the fact
that we are retrieving an existing document and then adding to it and updating.

Now, if we eliminate the updating and simply add each item as a new document (which we did
just to test but won't be adequate for our running system), then we still see a slight trend
upward in memory usage and the following images show that now most of the  memory is consumed
in char[] rather than the byte[] we saw before.  We don't know if this is normal and expected,
or if it is something to be concerned about as well.

http://tinypic.com/view.php?pic=vfgkyt&s=5

Any thoughts?

-----Original Message-----
From: Michael McCandless [mailto:lucene@mikemccandless.com]
Sent: Thursday, April 29, 2010 2:07 PM
To: java-user@lucene.apache.org
Subject: Re: IndexWriter and memory usage

OK I think you may be hitting this:

    https://issues.apache.org/jira/browse/LUCENE-2422

Since you have very large docs, the reuse that's done by
IndexInput/Output is tying up alot of memory.

Ross can you try the patch I just attached on that issue (merge it w/
the other issues) and see if that fixes it?  Thanks.

Mike

On Thu, Apr 29, 2010 at 11:58 AM, Woolf, Ross <Ross_Woolf@bmc.com> wrote:
> I ported the patch to 2.9.2 dev but it did not seem to help.  Attached is my port of
the patch.  This patch contains both 2283 and 2387, both of which I have applied in trying
to resolving this issue.
>
> -----Original Message-----
> From: Michael McCandless [mailto:lucene@mikemccandless.com]
> Sent: Tuesday, April 27, 2010 4:40 AM
> To: java-user@lucene.apache.org
> Subject: Re: IndexWriter and memory usage
>
> Oooh -- I suspect you are hitting this issue:
>
>    https://issues.apache.org/jira/browse/LUCENE-2283
>
> Your 3rd image ("fdt") jogged my memory on this one.  Can you try
> testing the trunk JAR from after that issue landed?  (Or, apply that
> patch against 3.0.x -- let me know if it does not apply cleanly and
> I'll try to back port it).
>
> But: it's spooky that you cannot repro this issue in your dev
> environment.  Are you matching the # thread and exact sequence of
> docs?
>
> Mike
>
> On Mon, Apr 26, 2010 at 4:14 PM, Woolf, Ross <Ross_Woolf@bmc.com> wrote:
>> We are still plagued by this issue.  I tried applying the patch mentioned but this
did not resolve the issue.
>>
>> I once tried to attach images from the heap dump to send out to the group but the
server removed them so I have posted the images on a public service with links this time.
 I would appreciate someone looking at them to see if they provide any insight into what is
occurring with this issue.
>>
>> When you follow the link click on the image and then once you see the image click
on a link in the lower left hand corner that says "View Raw Image."  This will let you view
the images at 100% resolution.
>>
>> This first image shows what we are seeing within VisualVM in regards to the memory.
 As you can see, over time the memory gets consumed.  Finally we are at a point where there
is no more memory available.
>> Graph
>> http://tinypic.com/view.php?pic=2ltk0h3&s=5
>>
>> This second image in VisualVM shows the classes sorted by size.  As you can see,
about 70% of all memory is consumed in the bytes array.
>> Bytes
>> http://tinypic.com/view.php?pic=s10mqs&s=5
>>
>> This third image is where the real info is.  This is where one of the bytes is being
examined and the option to go to nearest GC is chosen.  What you see here is what the majority
of the bytes show if selected, so this one is representative of most all.  As you can see
this one byte is associated with the index writer as you look at the chain of objects (and
thus so too are all the other bytes that have not been released for GC).
>> Garbage Collection
>> http://tinypic.com/view.php?pic=5obalj&s=5
>>
>> I'm hoping that as you look at this that it might mean something to you or give you
a clue as to what is holding on to all the memory.
>>
>> Now the mysterious thing in all of this is that our use of Lucene has been developed
into a "plug-in" that we use within an application that we have.  If I just run JUnit tests
around this plugin, indexing some of the same files that the actual application is indexing,
I cannot ever get the memory loss in my dev environment.  Everything seems to work as expected.
 However, once we are in our real situation, then we see this behavior.  Because of this I
would expect that the problem lays with the application, but once we examine the heap dumps
it then goes back to showing that the consumed bytes are "owned" by the index writer process.
 It makes no sense to me that we see this as we do, but none the less we do.  We see that
the Index Writer process is hanging onto a lot of data in byte arrays and it doesn't ever
seam to release it.
>>
>> In addition, we would love to show this to someone via a webex if that would help
in seeing what is going on.
>>
>> Please, any help appreciated and any suggestions on how to resolve or even troubleshoot.
 I can provide an actual heap dump but it is 63mb in size (compressed) so we would need to
work out some FTP where we can provide it if someone is willing to look at it in VisualVM
(or any other profiling tool).
>>
>> BTW - If we open and close the index writer on a regular basis then we don't run
into this problem.  It is only when we run continuously with an open index writer that we
do see this problem (we altered the code to open/close the writer a lot, but this slows things
down, so we don't want to run like this, but we wanted to test the behavior if we did so).
>>
>> Thanks,
>> Ross
>>
>> -----Original Message-----
>> From: Michael McCandless [mailto:lucene@mikemccandless.com]
>> Sent: Wednesday, April 14, 2010 2:52 PM
>> To: java-user@lucene.apache.org
>> Subject: Re: IndexWriter and memory usage
>>
>> Run this:
>>
>>    svn co https://svn.apache.org/repos/asf/lucene/java/branches/lucene_2_9
>> lucene.29x
>>
>> Then apply the patch, then, run "ant jar-core", and in that should
>> create the lucene-core-2.9.2-dev.jar.
>>
>> Mike
>>
>> On Wed, Apr 14, 2010 at 1:28 PM, Woolf, Ross <Ross_Woolf@bmc.com> wrote:
>>> How do I get to the 2.9.x branch?  Every link I take from the Lucene site takes
me to the trunk which I assume is the 3.x version.  I've tried to look around svn but can't
find anything labeled 2.9.x.  Is there a daily build of 2.9.x or do I need to build it myself.
 I would like to try out the fix you put into it, but I'm not sure where I get it from.
>>>
>>> -----Original Message-----
>>> From: Michael McCandless [mailto:lucene@mikemccandless.com]
>>> Sent: Wednesday, April 14, 2010 4:12 AM
>>> To: java-user@lucene.apache.org
>>> Subject: Re: IndexWriter and memory usage
>>>
>>> It looks like the mailing list software stripped your image attachments...
>>>
>>> Alas these fixes are only committed on 3.1.
>>>
>>> But I just posted the patch on LUCENE-2387 for 2.9.x -- it's a tiny
>>> fix.  I think the other issue was part of LUCENE-2074 (though this
>>> issue included many other changes) -- Uwe can you peel out just a
>>> 2.9.x patch for resetting JFlex's zzBuffer?
>>>
>>> You could also try switching analyzers (eg to WhitespaceAnalyzer) to
>>> see if in fact LUCENE-2074 (which affects StandandAnalyzer, since it
>>> uses JFlex) is [part of] your problem.
>>>
>>> Mike
>>>
>>> On Tue, Apr 13, 2010 at 6:42 PM, Woolf, Ross <Ross_Woolf@bmc.com> wrote:
>>>> Since the heap dump was so big and can't be attached, I have taken a few
screen shots from Java VisualVM of the heap dump.  In the first image you can see that at
the time our memory has become very tight most of it is held up in bytes.  In the second image
I examine one of those instances and navigate to the nearest garbage collection root.  In
looking at very many of these objects, they all end up being instantiated through the IndexWriter
process.
>>>>
>>>> This heap dump is the same one correlating to the infoStream that was attached
in a prior message.  So while the infoStream shows the buffer being flushed, what we experience
is that our memory gets consumed over time by these bytes in the IndexWriter.
>>
>>>>
>>>> I wanted to provide these images to see if they might correlate to the fixes
mentioned below.  Hopefully those fixes mentioned below have rectified this problem.  And
as I state in the prior message, I'm hoping these fixes are in a 2.9x branch and hoping for
someone to point me to where I can get those fixes to try out.
>>>>
>>>> Thanks
>>>>
>>>> -----Original Message-----
>>>> From: Woolf, Ross [mailto:Ross_Woolf@BMC.com]
>>>> Sent: Tuesday, April 13, 2010 1:29 PM
>>>> To: java-user@lucene.apache.org
>>>> Subject: RE: IndexWriter and memory usage
>>>>
>>>> Are these fixes in 2.9x branch?  We are using 2.9x and can't move to 3x just
yet.  If so, where do I specifically pick this up from?
>>>>
>>>> -----Original Message-----
>>>> From: Lance Norskog [mailto:goksron@gmail.com]
>>>> Sent: Monday, April 12, 2010 10:20 PM
>>>> To: java-user@lucene.apache.org
>>>> Subject: Re: IndexWriter and memory usage
>>>>
>>>> There is some bugs where the writer data structures retain data after
>>>> it is flushed. They are committed as of maybe the past week. If you
>>>> can pull the trunk and try it with your use case, that would be great.
>>>>
>>>> On Mon, Apr 12, 2010 at 8:54 AM, Woolf, Ross <Ross_Woolf@bmc.com> wrote:
>>>>> I was on vacation last week so just getting back to this...  Here is
the info stream (as an attachment).  I'll see what I can do about reducing the heap dump (It
was supplied by a colleague).
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: Michael McCandless [mailto:lucene@mikemccandless.com]
>>>>> Sent: Saturday, April 03, 2010 3:39 AM
>>>>> To: java-user@lucene.apache.org
>>>>> Subject: Re: IndexWriter and memory usage
>>>>>
>>>>> 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)?
>>>>>
>>>>> Mike
>>>>>
>>>>> On Fri, Apr 2, 2010 at 5:28 PM, Woolf, Ross <Ross_Woolf@bmc.com>
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 [mailto:lucene@mikemccandless.com]
>>>>>> Sent: Thursday, April 01, 2010 5:21 PM
>>>>>> To: java-user@lucene.apache.org
>>>>>> 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 <Ross_Woolf@bmc.com>
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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>>>>>>
>>>>>>
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>>>>>>
>>>>>>
>>>>>
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>>>>>
>>>>>
>>>>>
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>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> Lance Norskog
>>>> goksron@gmail.com
>>>>
>>>> ---------------------------------------------------------------------
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>>>>
>>>>
>>>>
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>>>>
>>>
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>>>
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>>>
>>
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