CF 8 JVM memory is not being garbage collected.

Question

I am baffled by something I am seeing on my QA server. I have
an app that we load tested but when the test completed the JVM
memory used was not released. I used CF Server Monitor to watch the
memory usage and sometimes it spiked to the max and either the app
failed or I got timeout exceptions.
This is the only app running on this server and the testing
completed over an hour ago but the memory has not been released
yet.
CF Admin settings:
Maximum JVM Heap Size (MB) 512
The CF Server JVM Setting arguments include: -server
-Dsun.io.useCanonCaches=false -XX:MaxPermSize=192m
-XX:+UseParallelGC
I found a script that uses java.lang.Runtime and
java.lang.management.managementFactory that dumps a JVM memory
usage profile The latest dump follows:
JVM Monitor - ColdFusion Server - Enterprise v8,0,1,195765
JVM Memory Monitor - struct
Heap Memory Usage - Committed 481 MB
Heap Memory Usage - Initial 0.00 MB
Heap Memory Usage - Max 493 MB
Heap Memory Usage - Used 437 MB
JVM - Free Memory 44.0 MB
JVM - Max Memory 493 MB
JVM - Total Memory 481 MB
JVM - Used Memory 449 MB
Memory Pool - Code Cache - Used 8.80 MB
Memory Pool - PS Eden Space - Used 6.37 MB
Memory Pool - PS Old Gen - Used 428 MB
Memory Pool - PS Perm Gen - Used 52.4 MB
Memory Pool - PS Survivor Space - Used 3.50 MB
Non-Heap Memory Usage - Committed 62.8 MB
Non-Heap Memory Usage - Initial 18.3 MB
Non-Heap Memory Usage - Max 240 MB
Non-Heap Memory Usage - Used 61.2 MB
According to the CF Server Monitor JVM memory usage builds up
to 477 MB then the app fails or timesout.
Session Scope memory usage: 0.27 KB
Application Scope memory usage: 1.370 KB
Server Scope memory usage: 3.12 KB
Since the test ended JVM Memory Usage has dropped back to 438
MB?
Besides CFAdmin nothing else is running on this CF Server.
I've read several other memory related topics but none of them have
helped.
Can someone tell me why the memory isn't being release? How
can I further troubleshoot the problem?
Thx
pwp

Answer 1

> Adam Cameron wrote:
>
The maximum stable heap size I've managed to get is around
> 1.0-1.2GB, on a win32 system. On Solaris (running a
32-bit JVM),
> about 1.4GB. It *seems* like GC doesn't actually clear
out RAM
> properly if more than that much RAM is being
addressed.
>
> Yes, there is a well-known
>
http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_19359&sliceId=1
Not really what I was talking about. One might be able to get
the CF
instance to *start* with 1.8GB allocated to the heap, but it
won't actually
work. I've managed to get a server to idle for a reasonable
length of time
on 1.5GB, but as soon as the thing started to ramp up, it
face-planted,
once it started actually trying to *use* the higher end of
the RAM
allocated to it. At 1.2GB, it'll seem to run OK for a
reasonable length of
time, but eventually it starts leaking memory; at around 1GB,
it was pretty
stable.
Hence my comment about it being *stable* at that allocation.
Not that "it
simply won't start if more than 1.8GB is allocated to it".
My point was that your rule of thumb:
maximum heap size(Xmx) = RAM(in MB) / (2 * number of servers
using the
JVM)
Is not a very good one. Plug 4GB RAM (so a small server) and
one CF
instance into that equation. Your rule suggests I should be
allocating 2GB
to the heap. Which - as you yourself pointed out - won't
work.
Adam