I always hold this as a ground rule:
Increase heapsize as much as possible as long as:
latency goals are met (gc does note take too long)
enough memory is spared for system and vm. (enough to compensate for
spikes, watch your swap usage to determine this)
hope this helps a bit
Peter Crowther wrote:
From: Robinson, Eric [eric.robin...@psmnv.com]
Is there a way to tell what the optimal
heap size is for our application, and whether the current small size is
effecting performance (aside from trial-and-error or repeated
benchmarking with tools like jmeter)?
Smaller heap sizes may lead to more frequent garbage collection, which costs CPU cycles*
and hence affects performance. If your app is spending much of its time in the garbage
collector, increasing heap would help - but it's then a process of trial-and-error to
work out what the "optimal" size is, as it's a trade-off between %CPU spent in
garbage collection and memory.
As a sketch, I'd turn on some of the GC monitoring in the virtual machine and
see if you can get a feel for how much time it's spending in the GC. Most of
my apps are well below 1%, though I have one (.Net app) that spends c. 98% of
its time in the GC as it loads state from disk.
You also need to decide what's "good enough". The difference in "real-world"
performance between spending 0.1% and 1% in the GC is negligible; the difference between 10% and
90% is rather obvious!
- Peter
* Some of the cycles would be spent no matter when the garbage happened to be
collected; others are overhead each time, though GC algorithms have improved a
lot and the overhead's far lower than it used to be.
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