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

[Alexey Ragozin]

Exactly.

I'm polling JMX regularly to catch LastGCInfo for every collection
(not ideal solution though). LastGCInfo have all in need (I'm mostly
interested in STW pauses and allocation / reclaim rates).

There are some limitations - I cannot reproduce tenuring distribution
from JMX, CMS fragmentation metrics also available only through logs
(very unfortunate).

Regards,
Alexey

On Mon, Apr 23, 2012 at 8:13 AM, the.6th.month at gmail.com
<the.6th.month at gmail.com> wrote:
>> 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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>>
>>