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From "Khawaja Shams" <kssh...@gmail.com>
Subject Re: lucene nicking my memory ?
Date Thu, 04 Dec 2008 08:47:31 GMT
Magnus,     Please feel free to ignore my last email; I see that you had
this setup earlier.  As far as using up all the memory it can get its hands
on, this is actually a good thing. This allows Lucene and other java
applications to keep more things in cache when more memory is available.
Also, if you throw more memory at the program, the GC will try to spend
little effort in cleaning up until it is necessary. By setting xmx to 1536M,
you are effectively telling the jvm that you have this much memory available
for the java program.  Therefore, there is no reason for the GC to waste any
more resources when the program is taking 1300M of ram. I think you should
not worry until you start throwing OOMEs even after you have allocated the
1536M.


Is the program still responsive even after it hits the "peak" memory
utilization? You said that the gc request was not being honored, but it is
unclear if the queries are returning at that point.  Lastly, I highly
recommend against ever making the gc requests.



Regards,
Khawaja Shams

On Thu, Dec 4, 2008 at 12:30 AM, Khawaja Shams <ksshams@gmail.com> wrote:

> Magnus,   If you get a chance, can you try setting a different xms and xmx
> value. For instance, try xms384M and xmx1024M.
>
>
>  The "forced" GC [request] will almost always reduce the memory footprint
> simply because of the weak references that lucene leverages, but I bet
> subsequent queries are not as fast and you basically need to warm up your
> server after the GC (which would boost up the footprint again :) ).
>
>
>
> Regards,
> Khawaja
>
>
> On Wed, Dec 3, 2008 at 10:27 PM, Magnus Rundberget <rundis@mac.com> wrote:
>
>> Well...
>>
>> after various tests I downgraded to lucene 1.9.1 to see if that had any
>> effect... doesn't seem that way.
>>
>> I have set up a JMeter test with 5 concurrent users doing a search (a
>> silly search for a two letter word) every 3 seconds (with a random of +/-
>> 500ms).
>>
>> - With 512 MB xms/xmx memory usage settles between 400/500 after a few
>> iterations, but no OOME.
>> At the end of the run memory settles usually between 200-300 somewhere
>> (really depends), but no cleanup occurs for minutes ...unless I do a forced
>> GC.
>>
>> - Did the same run with 384MB and hit 2 OOME
>>
>> - Did the same run with 256MB and hit 5 or 6 OOME
>>
>> Tried to run tomcat with jdk 1.6 and -server option as well, but didn't
>> seem to help at all either.
>>
>> The finally I ran the test scenario above but with 1536MB xms/xmx... and
>> guess what. It used it all pretty quickly. It used between 1000-1400/1500
>> for most of the run. At the end of the run memory usage settled at about 750
>> MB ... until I did a forced gc.
>> This do bother me, if the solution could have been to throw more memory at
>> the problem I could live with that, but it just seems to consume all memory
>> it can get it hands on (:-
>> Is there any way to limit the memory usage in Lucene (configuration) ?
>>
>> Im obviously not sure if lucene is the culprit as Im using spring (2.5) ,
>> hibernate (3.3) and open session in view and lots of other stuff etc in my
>> app. So I guess my next step would be to create a very limited web app with
>> just a servlet calling the lucene api.Then do some profiling on that.
>>
>> cheers
>> Magnus
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On 3. des.. 2008, at 14.45, Michael McCandless wrote:
>>
>>
>>> Are you actually hitting OOME?
>>>
>>> Or, you're watching heap usage and it bothers you that the GC is taking a
>>> long time (allowing too much garbage to use up heap space) before sweeping?
>>>
>>> One thing to try (only for testing) might be a lower and lower -Xmx until
>>> you do hit OOME; then you'll know the "real" memory usage of the app.
>>>
>>> Mike
>>>
>>> Magnus Rundberget wrote:
>>>
>>>  Sure,
>>>>
>>>> Tried with the following
>>>> Java version: build 1.5.0_16-b06-284 (dev), 1.5.0_12 (production)
>>>> OS : Mac OS/X Leopard(dev) and Windows XP(dev), Windows 2003
>>>> (production)
>>>> Container : Jetty 6.1 and Tomcat 5.5 (latter is used both in dev and
>>>> production)
>>>>
>>>>
>>>> current jvm options
>>>> -Xms512m -Xmx1024M -XX:MaxPermSize=256m
>>>> ... tried a few gc settings as well but nothing that has helped (rather
>>>> slowed things down)
>>>>
>>>> production hw running 2 XEON dual core processors
>>>>
>>>> in production our memory reaches the 1024 limit after a while (a few
>>>> hours) and at some point it stops responding to forced gc (using jconsole).
>>>>
>>>> need to digg quite a bit more to figure out the exact prod settings. But
>>>> safe to say the memory usage pattern can be recreated on different hardware
>>>> configs, with different os's, different 1.5 jvms and different containers
>>>> (jetty and tomcat).
>>>>
>>>>
>>>>
>>>> cheers
>>>> Magnus
>>>>
>>>>
>>>>
>>>> On 3. des.. 2008, at 13.10, Glen Newton wrote:
>>>>
>>>>  Hi Magnus,
>>>>>
>>>>> Could you post the OS, version, RAM size, swapsize, Java VM version,
>>>>> hardware, #cores, VM command line parameters, etc? This can be very
>>>>> relevant.
>>>>>
>>>>> Have you tried other garbage collectors and/or tuning as described in
>>>>> http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html?
>>>>>
>>>>> 2008/12/3 Magnus Rundberget <rundis@mac.com>:
>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> We have an application using Tomcat, Spring etc and Lucene 2.4.0.
>>>>>> Our index is about 100MB (in test) and has about 20 indexed fields.
>>>>>>
>>>>>> Performance is pretty good, but we are experiencing a very high usage
>>>>>> of
>>>>>> memory when searching.
>>>>>>
>>>>>> Looking at JConsole during a somewhat silly scenario (but illustrates
>>>>>> the
>>>>>> problem);
>>>>>> (Allocated 512 MB Min heap space, max 1024)
>>>>>>
>>>>>> 0. Initially memory usage is about 70MB
>>>>>> 1. Search for word "er", heap memory usage goes up by 100-150MB
>>>>>> 1.1 Wait for 30 seconds... memory usage stays the same (ie no gc)
>>>>>> 2. Search by word "og", heap memory usage goes up another 50-100MB
>>>>>> 2.1 See 1.1
>>>>>>
>>>>>> ...and so on until it seems to reach the 512 MB limit, and then a
>>>>>> garbage
>>>>>> collection is performed
>>>>>> i.e garbage collection doesn't seem to occur until it "hits the roof"
>>>>>>
>>>>>> We believe the scenario is similar in production, were our heap space
>>>>>> is
>>>>>> limited to 1.5 GB.
>>>>>>
>>>>>>
>>>>>> Our search is basically as follows
>>>>>> ----------------------------------------------
>>>>>> 1. Open an IndexSearcher
>>>>>> 2. Build a Boolean Query searching across 4 fields (title, summary,
>>>>>> content
>>>>>> and daterangestring YYYYMMDD)
>>>>>> 2.1 Sort on title
>>>>>> 3. Perform search
>>>>>> 4. Iterate over hits to build a set of custom result objects (pretty
>>>>>> small,
>>>>>> as we dont include content in these)
>>>>>> 5. Close searcher
>>>>>> 6. Return result objects.
>>>>>>
>>>>>
>>>>> You should not close the searcher: it can be shared by all queries.
>>>>> What happens when you warm Lucene with a (large) number of queries: do
>>>>> things stabilize over time?
>>>>>
>>>>> A 100MB index is (relatively) very small for Lucene (I have indexes
>>>>>
>>>>>> 100GB). What kind of response times are you getting, independent
of
>>>>>>
>>>>> memory usage.
>>>>>
>>>>> -glen
>>>>>
>>>>>
>>>>>> We have tried various options based on entries on this mailing list;
>>>>>> a) Cache the IndexSearcher - Same results
>>>>>> b) Remove sorting - Same result
>>>>>> c) In point 4 only iterating over a limited amount of hits rather
than
>>>>>> whole
>>>>>> collection - Same result in terms of memory usage, but obviously
>>>>>> increased
>>>>>> performance
>>>>>> d) Using RamDirectory vs FSDirectory - Same result only initial heap
>>>>>> usage
>>>>>> is higher using ramdirectory (in conjuction with cached indexsearcher)
>>>>>>
>>>>>>
>>>>>> Doing some profiling using YourKit shows a huge number of char[],
>>>>>> int[] and
>>>>>> string[], and ever increasing number of lucene related objects.
>>>>>>
>>>>>>
>>>>>>
>>>>>> Reading through the mailing lists, suspicions are that our problem
is
>>>>>> related to ThreadLocals and memory not being released. Noticed that
>>>>>> there
>>>>>> was a related patch for this in 2.4.0, but it doesn't seem to help
us
>>>>>> much.
>>>>>>
>>>>>> Any ideas ?
>>>>>>
>>>>>> kind regards
>>>>>> Magnus
>>>>>>
>>>>>> ---------------------------------------------------------------------
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>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>>
>>>>> -
>>>>>
>>>>> ---------------------------------------------------------------------
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>>>>> For additional commands, e-mail: java-user-help@lucene.apache.org
>>>>>
>>>>>
>>>>
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>>>>
>>>>
>>>
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>>>
>>>
>>
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>>
>

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