Re: [Wrapper-user] JVM hang - Xms / Xmx

[Paul C. <cas...@au...>]

Thanks Leif.

We have 6.3GB of RAM in a Win2K Advanced Server box - usually around 3GB
free, so there's no chance of running out of physical RAM.

We were using:
# Initial Java Heap Size (in MB)
wrapper.java.initmemory=1600

# Maximum Java Heap Size (in MB)
wrapper.java.maxmemory=1600


Now using:
# Initial Java Heap Size (in MB)
wrapper.java.initmemory=1400

# Maximum Java Heap Size (in MB)
wrapper.java.maxmemory=1600

When first trying the change, I tried initmemory=1200, then 1300, now 1400
just to make sure it was functioning ok.  In the Windows Task Manager the
Java process always peaked closed to each of these figures - never exceeded
1600MB as it did previously (used to get up to 1780MB: 1600MB + JVM
overhead I assume).

I've seen this hotspot error once before since switching to JSW (months
back) - before hand it probably would have just been lost (svrany - MS
product) - yay for JSW I say.

Once again I don't seem to be able to find anything concrete about this
error in Sun's Java forums, other than suggestions that native font dll's
may have become corrupt - but then one would expect the error to occur
regularly.  It happened twice in one day last week, and then today, with
varying durations between the java.lang.OutOfMemoryError's and the JVM
crash.  They've both been there each time though.

We had always previously set the min and max heap values to the same.  I
couldn't find much Sun info on how Xms and Xmx alter the behaviour of
garbage collection (or any other behaviour for that matter) - only in
http://java.sun.com/docs/hotspot/gc/.  I just gave it a whirl and it seems
to have made a difference to the JVM hanging.

I also read in one of the forums that issues with native calls from the JVM
were rectified in 1.4.1_02 +.  Have you also heard this?

Regards,

Paul Casanova




|---------+---------------------------------------->
|         |           Leif Mortenson               |
|         |           <le...@ta...>    |
|         |           Sent by:                     |
|         |           wra...@li...|
|         |           ceforge.net                  |
|         |                                        |
|         |                                        |
|         |           31/03/2004 04:05 PM          |
|         |           Please respond to            |
|         |           wrapper-user                 |
|---------+---------------------------------------->
  >--------------------------------------------------------------------------------------------------------------|
  |                                                                                                              |
  |       To:       wra...@li...                                                           |
  |       cc:                                                                                                    |
  |       Subject:  Re: [Wrapper-user] JVM hang - Xms / Xmx                                                      |
  >--------------------------------------------------------------------------------------------------------------|




Paul,

Paul Casanova wrote:

>We've had problems with our JVM hanging from time to time.  The Wrapper
>restarted it each time faithfully, which saved heartache and downtime.
>
>I started looking into the initial / maximum heap values, and while I
>couldn't find much info about how they relate to garbage collection, there
>were comments that suggested setting them to different values (rather than
>the same).  I did this, and the JVM hasn't hung in the past 3 weeks -
which
>is fantastic!
>
>
Thanks for commenting on that.  I don't usually set the initial and max
heap values to
the same thing.  But I have seen config files from users in the past
which have done so.

Where did you see that?  It may make sense to place a warning in the
documentation
as something to keep an eye out for.

>Has this worked for anyone else - or is anyone else having JVM hanging
>issues?
>
>What I have noticed is that we are now getting
>INFO   | jvm 1    | 2004/03/31 12:26:33 | java.lang.OutOfMemoryError
>
>
What are the values that you are using for your initial and max heap
sizes?   My
obvious answer is that it appears that your application is running out
of memory.
But that would be too obvious.

When you modified the values for the max and init heap sizes are you
sure that
you do not have any typos that would be causing the wrapper to use the
defaults.
Check the command used to launch java at the top of the wrapper log with
debug
output enabled.  Make sure they are what you expect.

How long has your application been running when you encounter this problem?
Does there appear to be a memory leak in the application?   I can't think
of
any reason why this would be working with the init and max heap sizes set
to
the same values, but not working when they differ...

I'll think about this more after I hear back from you.

Cheers,
Leif



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