Two basic questions on -verbosegc and -XX:+PrintTenuringDistribution

[the.6th.month at gmail.com]

Hi, Alexey
looks pretty cool, so basically you are parsing LastGCInfo to get those
metrics, right?

Leon

On 23 April 2012 16:05, Alexey Ragozin <alexey.ragozin at gmail.com> wrote:

> Hi,
>
> If you need this information for monitoring, you can get it with JMX.
> Some time ago I have written tool displaying GC metrics (similar to GC
> log). It is using attach API and JMX to get data from JVM.
>
> It is available at
> http://code.google.com/p/gridkit/downloads/detail?name=gcrep.jar
> Usage: java -jar gcrep.jar <PID>
>
> But you probably will be more interested in sources, you can find them here
>
> http://code.google.com/p/gridkit/source/browse/branches/aragozin-sandbox/young-gc-bench/src/main/java/org/gridkit/util/monitoring/MBeanGCMonitor.java?spec=svn1461&r=1461
>
> Regards,
> Alexey
>
> > Date: Sun, 22 Apr 2012 22:24:31 +0200
> > From: Taras Tielkes <taras.tielkes at gmail.com>
> > Subject: Two basic questions on -verbosegc and
> >        -XX:+PrintTenuringDistribution
> > To: hotspot-gc-use at openjdk.java.net
> > Message-ID:
> >        <
> CA+R7V78bTOkvaYgwNCPC2MfiqdV-QBtOidz3nUXjb9bwZ5FrNg at mail.gmail.com>
> > Content-Type: text/plain; charset=ISO-8859-1
> >
> > Hi,
> >
> > We're using a time-series database to store and aggregate monitoring
> > data from our systems, including GC behavior.
> >
> > I'm thinking of adding two metrics:
> > * total allocation (in K per minute)
> > * total promotion (in K per minute)
> >
> > The gc logs are the source for this data, and I'd like to verify that
> > my understanding of the numbers is correct.
> >
> > Here's an example verbosegc line of output (we're running ParNew+CMS):
> > [GC 2136581.585: [ParNew:345951K->40960K(368640K), 0.0676780 secs]
> > 3608692K->3323692K(5201920K), 0.0680220 secs]
> >
> > a) The delta between the ParNew "before" and "after" is:
> 345951K-40960K=304991K
> > My understanding is that the 304991K is the total of (collected in
> > young gen + promoted to tenured gen)
> > Since this number of composed of two things, it's not directly useful by
> itself.
> >
> > b) The delta between the overall heap "before" and "after" is:
> > 3608692K-3323692K=285000K
> > I assume that this is effectively the volume that was collected in
> > this ParNew cycle.
> > Would it be correct to calculate the total allocation rate of the
> > running application (in a given period) from summing the total heap
> > deltas (in a given timespan)?
> >
> > I do realize that it's a "collected kilobytes" metric, but I think
> > it's close enough to be used as a "delayed" allocation number,
> > especially when looking at a timescale of 10 minutes or more.
> > It has the additional convenience of requiring to parse the current
> > gc.log line only, and not needing to correlate with the preceding
> > ParNew event.
> >
> > c) I take it that the difference between the two deltas (ParNew delta
> > and total heap delta) is effectively the promotion volume?
> > In the example above, this would give a promotion volume of
> > (345951K-40960K)-(3608692K-3323692K)=19991K
> >
> > d) When looking at -XX:+PrintTenuringDistribution output, I assume the
> > distribution reflects the situation *after* the enclosing ParNew event
> > in the log.
> >
> > Thanks in advance for any corrections,
> > -tt
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