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From "Robinson, Eric" <eric.robin...@psmnv.com>
Subject RE: Free Memory vs. Total Memory vs. Max Memory
Date Mon, 20 Feb 2012 15:36:41 GMT
> > What are the possible downsides of setting a low initial 
> memory pool 
> > and a high max pool? If a tomcat app usually needs 
> approximately 64MB 
> > of heap space, but sometimes as much as 300-400MB, would it 
> cause any 
> > problems to set the initial pool to 16M and the max pool to 512M?
> 
> An additional answer to your question:
> 
> If multiple JVMs need, in total, more RAM than the machine 
> has available at any given moment, the OS may allocate swap 
> memory to one or more of those processes.  Once a JVM is 
> moved into swap, it is difficult to predict when it will move 
> back out again.
> 
> For JVMs this is particularly bad, as internal memory 
> operations inside the process will take orders of magnitude 
> longer to complete.  This can negatively impact the timing of 
> garbage collection and lead to an increased risk of OOM, for 
> some collectors.
> 
> 

Thanks for the additional information. If what you described occurs, we
would see OOMs in the logs, correct? Also, if the machine has inadequate
RAM, then the effect you described could be the same whether you specify
a low or high -Xms value, correct?

--Eric





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