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From Wade Chandler <>
Subject Re: Java process growth under Linux...leak?
Date Tue, 31 Aug 2004 17:10:21 GMT
Wade Chandler wrote:

> Mark Maigatter wrote:
>> We have a Tomcat 5.0.25 based web site for uploading images and assorted
>> files and managing them.
>> We have found that the Java process that Tomcat is running under is
>> gradually growing when repetitively processing files uploaded and 
>> stripped
>> out of the form submissions by the Apache FileUpload component.  All 
>> signs
>> point to a memory leak?
>> Upon the submission of about 500 files we had a 31MB growth in the 
>> size of
>> the java process using "top".   
>> However, the Sun Java jvmstat shows that the Java heap is staying 
>> relatively
>> constant.  The "-gc" numbers fluctuate in a manner that shows reasonable
>> garbage collection activity and the total used across the s0/s1/eden/old
>> stay with the range for the initial numbers.
>> My question is what would you recommend to isolate the process growth?
>> Is there a way within Java to see the underlying process growth to help
>> isolate it in the processing cycle?
>> --mark
> How large were the files you were uploading?  I mean  you just said you 
> uploaded 500 files.  You should expect to see process memory growth. The 
> JVM has it's own object heap where it manages it's "internal" memory.  
> Then there is the process and it's memory which is a C heap.
> I see that you uploaded 500 files.  Were these one right after the 
> other, or were they close to simultaneous?  Also, how are you uploading 
> the files?  Are you using some type of a parser?  Are you using the 
> commons file upload control?  If the JVM reports good memory collection, 
> then there is no memory leak in Tomcat.  31MB of growth for a process 
> uploading 500 files shouldn't be that bad depending on how they were 
> uploaded and file sizes.
> Think about it. If the files were between 100kb and 60kb then you have a 
> total of 30mb to 50mb of memory just in that data alone not including 
> your application and other buffers you may or may not be creating while 
> uploading.
> For perforamnce reasons the VM isn't going to suddenly resize the heap 
> as soon as it frees a group of java objects because as far as it knows 
> you may come along and upload 50mb worth of data immediately after the 
> first.  This is a performance thing.  Resizing the heap takes time and 
> cpu resources and affects performance.  The VM will reuse this memory 
> over and over again.
> I would look at any loops I might have reading from the stream.  Do you 
> create a bunch of small byte array's while uploading the files?  Maybe 
> you could increase the buffer size, be sure to null them out after you 
> perform a read to tell them VM you are done with the variable now (for 
> when the vm collects), and then see if that affects the memory growth.   
> This should help speed the file upload a bit and get rid of some buffers 
> in loops a little quicker if you aren't nulling the array.  If however 
> you are simultaneously uploading much of this data, then a 31mb spike in 
> memory usage shouldn't be a suprise no matter what.
> Basically you can impose limits on the VM and you can use switches to do 
> this.  You can also devote more memory to eden or survivor objects so 
> that the VM can make better use of the most commonly used memory.  You 
> can find more info on this topic and others at this url:
> Many docs.  One for you might be:
> scroll down to the bottom and check out options:
> -XX:NewRatio
> -XX:NewSize
> -XX:SurvivorRatio
> Basically the defaults for the -server VM are to allow the best 
> performance for a multi user multi threaded application such as tomcat. 
>  So, unless you are running out of memory or you need to cripple the app 
> servers performance by limiting it's growth because you have a bunch of 
> other applications running on the same server, then I suggest sticking 
> with the defaults.
> Wade
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Just noticed you wrote about the upload component.  I haven't looked at 
that code's parse to see how it is handling reading bytes from the 
stream, but I'm sure there have been many eyes on it.  I would say this 
is probably just a memory usage over time issue (short period of time). 
  Use those links I gave you and play with the memory switches a bit to 
see if you can get some kind of a situation that works best for you. 
The switches:

Can make the vm resize the heap differently, but you will want to be 
careful.  You may make things very slow by messing with the defaults for 
those switches.


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