From: Charles Oliver Nutter <charles.nutter@...>
Date: 2009-01-27T15:00:26+09:00
Subject: [ruby-core:21596] Re: [Feature #1047] request: getters, setters for the GC

Thomas Enebo wrote:
> No reason MRI should not consider making their GC tunable IMHO.
> 
> I think GC tunables at startup or during runtime should be considered 
> implementation dependent.  Java has many different GCs.  Certainly not 
> all GC's have the same tunable parameters.  Even if they did would you 
> really expect a tunable to work on different GC impls as expected?

I'd expand this to point out that all Java's GCs have many, many 
possible settings as well, but almost all are configured at startup. 
There are very few settings that can be tweaked at runtime, for a couple 
reasons:

* Hotspot makes some decisions about how to allocate and reallocate heap 
space immediately at startup.
* Hotspot also adjust GC settings (heap ratios, tenuring rates, etc) 
based on runtime information. So tweaking things at runtime would be 
forcing profiled settings to be thrown out.

But in general, having some set of command-line configurable settings 
would be a great idea, if it could be done without a performance impact. 
JRuby users are becoming more accustomed to having many available config 
settings when they need them.

- Charlie