Recommended heap sizes for Dev/Live/Shared CF boxes

Question

Hi all
I've searched through all the relevant past posts, but most of them were posted before CF8.0.1 going 64-bit, so the situation has changed slightly.
What are people's opinions on heap sizes for various server setups? I have my dev server - I leave this on 512MB and that's fine for most of the stuff I do. We generally up this to a gig on our live servers (which only run 3-4 small sites), and historically we've not gone above this on our Shared servers (which host anywhere up to 400 sites) because of the 32-bit limit.
However, now we're running CF9 on 64-bit Server 2008, we've obviously got a lot more RAM available. The obvious choice is to ramp it up high, but I've also been heard that causes issues of its own - the Java GC then has far more work to do when it's called and as the memory fills it's harder to get a contiguous block of RAM, so performance can suffer.
Does anyone have any experience of running Shared servers, or busy sites? The Server monitor is great for tuning maximum threads and the suchlike, but I can't really sit in front of it for hours waiting for the heap to fill. Also, our live servers are only Standard edition, so there's no Server Monitor.
Thoughts?
Ta
O.

Answer 1

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I have my dev server - I leave this on 512MB and that's fine for
most of the stuff I do. We generally up this to a gig on our live
servers (which only run 3-4 small sites), and historically we've not
gone above this on our Shared servers (which host anywhere up to 400
sites) because of the 32-bit limit.
However, now we're running CF9 on 64-bit Server 2008, we've obviously got a lot more RAM available. The obvious choice is to ramp it up high, but I've also been heard that causes issues of its own - the Java GC then has far more work to do when it's called and as the memory fills it's harder to get a contiguous block of RAM, so performance can suffer.
Leave the memory setting at the default value, until testing requires you to do otherwise, or your sites unravel some unforeseen memory demand. It's a risk our SysAdmin colleagues are prepared to take. With the coming of 64-bit, they've been on the alert, and have always cattle-prodded us whenever we've been tempted to push the button to go higher.
Our defaults almost coincide with yours: 512 MB for 32-bit and just over 1GB for 64-bit. So what you yourself have just said is my own basic wisdom on the subject, too: if it aint broke, don't try to fix it.
[postscript: I work full-time at one company, part-time at another. By pure coincidence, both use the same JVM memory settings.]