Hi,
On 27.06.21 10:30, Stefan Reich wrote:
Hi,
in my <https://bea.gazelle.rocks/>application
<https://bea.gazelle.rocks> I have about 800 MB of live objects. I know
this because that's the used heap I get after running System.gc().
However, in normal operation (without calling System.gc()), heap use
hovers around 3 GB out of 6 GB. I'm using G1.
So my question is - since the garbage collector is supposed to "race"
the application threads anyway - can't it be made to "race to the end"?
Meaning, until no or almost no dead objects remain?
I am totally fine with this potentially lowering the overall application
or GC throughput; it's supposed to happen in irelatively (though not
completely!) idle phases.
Please give ZGC a try, it might give you exactly what you want here.
There are only a few very small STW pauses (<1 ms) per collection cycle
with it in jdk16/17.
I really can't afford the seconds-long stop-the world pause of
System.gc(). I just wish to put the regular backgruond GC on
steroids for a few seconds until its job is done >
Reasons?
Not sure exactly which reasons for which of the questions you expect
here, but one reason for why g1 system.gc() call (without
-XX:+ExplicitGCInvokesConcurrent) is that it's defined as a fully,
maximally compacting stw gc pause.
A. It just feels cleaner to have no more dead objects. (Gotta love the
clean feeling!)
Options with G1 are to
- enable -XX:+ExplicitGCInvokesConcurrent to get a concurrent marking
with subsequent incremental collections since you "are not completely
idle". This should give you lower pause times at least.
- maybe the functionality in
https://bugs.openjdk.java.net/browse/JDK-8204089 provides what you want
for g1.
B. We find out how much heap we are actually using - no chance of that
in normal operation.
MXBeans should give you a fairly good idea about that without an stw
full gc, particularly after a concurrent marking.
Thanks,
Thomas
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