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From Michael McCandless <luc...@mikemccandless.com>
Subject Re: IndexWriter and memory usage
Date Tue, 13 Apr 2010 09:36:10 GMT
The infoStream generally looks healthy.  You seem to have a contained
set of unique field names.

The one thing that's interesting is... your docs are quite large.  If
you grep for "flush: segment=" in your infoStream you see how many
docs "fit" in 16 MB before flushing, and it's lowish (as high as ~300
and as low as only 1).

The "only 1" case looks like it could be the cause of your OOME, ie,
there are some docs that are so large that indexing that 1 doc causes
IndexWriter to use too much RAM and then immediately flush... Lucene
cannot flush mid-document.  So this means IndexWriter will allocate
however much RAM is needed for a single document, and flush right
after that, very easily needing to exceed the 16 MB temporarily.

Can you test whether you are hitting OOME on certain specific [very
large] documents?  The worst case poison-pill document is one that has
many many unique terms.

Mike

On Mon, Apr 12, 2010 at 11:54 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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