What influences young generation pause times?

Raman Gupta rocketraman at fastmail.fm
Wed Apr 21 15:36:02 PDT 2010

On 04/21/2010 06:12 PM, Jon Masamitsu wrote:
> There is no shortage of good ideas for the GC team to work on.
> RuntimePermission might be another one, but the simple fact is
> that we don't have time to work on everything we should. Right
> now our top priorities are reliability, faster GC's and more
> predictable GC's. Anything else is a hard sell.

Thanks Jon.

I've never contributed to the JDK before, but I suspect that 
implementing the first phase of this particular feature as I described 
it would be very easy (basically just gate System.gc() with a new 
RuntimePermission). But before I go spend hours trying to figure out 
how to download and build the JDK, and contribute a patch, it would be 
nice to know if it has a good chance of being accepted.

Note that this goes directly towards the goal of predictable GCs. For 
example, one of my current server applications generally does one or 
two full GCs daily. Currently, that full GC takes about 3-4 seconds, 
but its timing is based solely on the size of the old gen, and is 
completely unpredictable -- it could occur in the middle of the night 
(good) or it could occur during peak time (bad). My solution would 
allow my app to schedule the full GC overnight (subject to the 
non-guaranteed constraints of System.gc, of course, but in practice 
System.gc seems to pretty reliably kick off a full GC), with which the 
app will almost certainly make it through the peak period without 
another full GC occurring.

I do of course understand there would be significant work involved by 
the GC team just to review and accept such a patch, so I completely 
understand if the answer is no.


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