What influences young generation pause times?

Jon Masamitsu jon.masamitsu at oracle.com
Wed Apr 21 15:56:42 PDT 2010


Raman,

Define this GC API for me.  Where is the API (Java class)?

Jon

 > Without such permission, the System.gc() call would simply return 
without doing anything. Ideally the signature would be
 > modified to return a boolean "true if performed", "false if not", and 
even more ideally, a more comprehensive GC API could be
 > provided.

On 04/21/10 15:36, Raman Gupta wrote:
> 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.
>
> Cheers,
> Raman



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