Clarity regarding GC stats

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Amit Saha

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Jul 5, 2017, 8:38:42 PM7/5/17
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Hi all,

linkerd's GC related statistics has these:

jvm:gc:msec 22787.0
jvm:gc:eden:pause_msec_count 2
jvm:gc:eden:pause_msec_sum 3
jvm:gc:eden:pause_msec_avg 1.5
jvm:gc:eden:pause_msec{quantile="0"} 1
jvm:gc:eden:pause_msec{quantile="0.5"} 1
jvm:gc:eden:pause_msec{quantile="0.9"} 2
jvm:gc:eden:pause_msec{quantile="0.95"} 2
jvm:gc:eden:pause_msec{quantile="0.99"} 2
jvm:gc:eden:pause_msec{quantile="0.999"} 2
jvm:gc:eden:pause_msec{quantile="0.9999"} 2
jvm:gc:eden:pause_msec{quantile="1"} 2
jvm:gc:ParNew:msec 22174.0
jvm:gc:ParNew:cycles 17882.0
jvm:gc:ConcurrentMarkSweep:msec 613.0
jvm:gc:ConcurrentMarkSweep:cycles 57.0
jvm:gc:cycles 17939.0


Is there a document where I can understand what these metrics stand for?

Thanks,
Amit.



Kevin Lingerfelt

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Jul 5, 2017, 9:28:34 PM7/5/17
to Amit Saha, linkerd-users
Hey Amit,

There's a brief writeup about the JVM stats that are exported here:


If you're looking for more in-depth explanation, I'd recommend checking out the code comments from where these stats are collected, here:


Hope that helps,
Kevin

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Amit Saha

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Jul 5, 2017, 9:55:49 PM7/5/17
to Kevin Lingerfelt, linkerd-users
On Thu, Jul 6, 2017 at 11:28 AM Kevin Lingerfelt <k...@buoyant.io> wrote:
Hey Amit,

There's a brief writeup about the JVM stats that are exported here:


If you're looking for more in-depth explanation, I'd recommend checking out the code comments from where these stats are collected, here:


Hope that helps,
Kevin

It does, thanks Kevin. In general, is there any documentation/data/things to know of  about linkerd + garbage collection? I imagine that would be a common question. (https://www.reddit.com/r/kubernetes/comments/6e7hz5/linkerd_vs_envoy/)



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William Morgan

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Jul 6, 2017, 4:40:22 PM7/6/17
to Amit Saha, Kevin Lingerfelt, linkerd-users
Hey Amit,

There's a lot of documentation out there about the JVM GC generally. In terms of linkerd specifically, you shouldn't have to know too much unless you're pumping more than ~20k RPS through a single instance, in which case we start recommending some different GC tuning params. (See e.g. https://discourse.linkerd.io/t/linkerd-performance/146/5)



-William

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Amit Saha

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Jul 6, 2017, 8:06:41 PM7/6/17
to William Morgan, Kevin Lingerfelt, linkerd-users
Thank you William. I think that link is a good start.

Best Wishes,
Amit.


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