CMS collection keep working during holiday

[Y Srinivas Ramakrishna]

Hi Ken --

> 
> You are correct. 
> 
> I use this option set to find out how large is my lived objects:
> 
> -Xmx1536M -Xms1536M -XX:NewSize=256M -XX:MaxNewSize=256M
> -XX:+ExplicitGCInvokesConcurrent
> 
> (Yes, pressing Full-GC in jconsole or call System.gc() in application 
> can
> have same effect.)

A word of caution, re the differences between a concurrent collection and
a mark-compact collection as discussed earlier... Note that ExplicitGCInvokesConcurrent
will upon a System.gc() or jconsole/FullGC precipitate a concurrent
collection, not a mark-compact collection (which you would get in
the absence of the ExplicitGCInvokesConcurrent flag) when using the
CMS collector.

> 
> The application will daily reset all lived objects at 9:00am(holiday or
> non-trading day will not). Day open at 9:30am and day end at 4:30pm. From
> jconsole, I can see the heap chart raise steadily from 80M(9:30am) to
> 5xxM(4:30pm), if use the vm options above.

Ah, that is an important data point, because it seems to imply that
at least when trading is not in session, CMS collection behaves like
mark-compact collection in terms of reclaiming space... 

-- ramki

> 
> 
> 
> Y Srinivas Ramakrishna wrote:
> > 
> > 
> > Let me see if i understood that:-
> > 
> >> What the application is simply a stock quote client server and store
> >> daily
> >> stock quote and chart data in memory. The lived objects need around 
> 80M
> >> memory at day open and 500M memory at day end.
> > 
> > So you expect that the long-lived objects that will eventually get
> > promoted into the old generation, will start out at about 80 MB
> > at the start of the trading day and will end up about 500 MB at the
> > end of the trading day.
> > 
> > What happens at the end of the trading day? Do you discard the entire
> > table, so that the set of long-lived objects would be expected to shrink
> > back to 80 MB after the trading day ends?
> > 
> > If I understood your problem correctly (and correct me if i am wrong)
> > you find that the old gen occupancy does not shrink down with
> > concurrent collections at the end of the trading day, but shrinks only
> > upon a mark-compact collection (which typically happens as a result 
> of
> > a promotion failure).
> > 
> > (Loud thinking: I am assuming that the same effect would be achieved
> > by calling a System.gc() at the end of the trading day after the
> > table of quotes has been dropped. Of course, we need to figure out
> > why CMS may not reclaim the table even though it has been dropped.]
> > 
> > Please correct any misunderstanding of the situation.
> > -- ramki
> >  
> >> 
> >> y.s.ramakrishna wrote:
> >> > 
> >> > 
> >> > Could you run with the additional option +PrintReferenceGC and 
> see if
> >> > it sheds additional light on the problem? (Please share the resulting
> >> > GC logs.)
> >> > 
> >> > If at all possible, you might try rev'ing down to 6.0 and seeing
> >> > if the same behaviour reproduces or not?
> >> > 
> >> > I understand that some or all of this may not be possible in a
> >> > production setting.
> >> > 
> >> > -- ramki
> >> > 
> >> > ----- Original Message -----
> >> > From: "Ken-- at newsgroupstats.hk" <dragonken at gmail.com>
> >> > Date: Tuesday, October 7, 2008 10:17 pm
> >> > Subject: Re: CMS collection keep working during holiday
> >> > To: hotspot-gc-dev at openjdk.java.net
> >> > 
> >> > 
> >> >> Follow up to the jconsole above. This gif is captured today. You 
> 
> >> can 
> >> >> see the
> >> >> first CMS after a FULL GC is working. The 2nd one is working too 
> 
> >> but the
> >> >> memory free from 2nd generation is much less than the first CMS. 
> The
> >> >> memory
> >> >> free by 3rd CMS is further decreased.
> >> >> 
> >> >> The 5th CMS cannot free enough memory to make occanpcy in 
> old-gen 
> >> to less
> >> >> than 70%. So, continue non-stopping CMS happen again until a 
> Full GC
> >> >> (triggered by Concurrent Mode Failure).
> >> >> 
> >> >> http://www.nabble.com/file/p19872463/jconsole_20081008.jpg 
> >> >> 
> >> >> 
> >> >> 
> >> >> 
> >> >> 
> >> >> 
> >> >> -- 
> >> >> View this message in context:
> >> >>
> >> http://www.nabble.com/CMS-collection-keep-working-during-holiday-tp19773575p19872463.html
> >> >> Sent from the OpenJDK Hotspot Garbage Collection mailing list 
> >> archive 
> >> >> at Nabble.com.
> >> >> 
> >> > 
> >> > 
> >> 
> >> -- 
> >> View this message in context:
> >> http://www.nabble.com/CMS-collection-keep-working-during-holiday-tp19773575p19872900.html
> >> Sent from the OpenJDK Hotspot Garbage Collection mailing list 
> archive 
> >> at Nabble.com.
> >> 
> > 
> > 
> 
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>