Weird values for GC PS Marksweep / time collecting garbage

Troubleshooting
1

CMK version: Enterprise 2.1.0p38
OS version: Ubuntu 20.04

(the deployed mk_jolokia agent is also 2.1.0p38 / Java is v 17)

I am working with an inherited Check_MK installation. The mk_jolokia data for JVM GC PS MarkSweep shows a baseline metric of 200 - 500%. When a JVM goes into cycles of full GC, this metric rises to more than 4000%.

Leaving aside the fact that the absolute value is nonsense, the relative values do reflect the underlying health. However Check_MK does not allow me to set a threshold greater than 101%.

Has anyone else encountered this?

Is there a solution?

2

Yes i got the same.
As i understand code, it not a absolute value, but a rate.

i understand like that
Garbage collections: 0.01/s mean that it does 0.01 GC collector/s more than last period (60s)
Time spent collecting garbage: 2.12 % mean it increase time in GC of 2.12% comparing to last period.

It explain why it can higher than 100%

But i still cannot use it as the wato doesnā€™t allow more than 100%.

I end up by writing a custom plugin for Garbage Collector

3

Thank you.

Your confirmation confirms that Iā€™m not completely crazy.

4

iā€™ve just done a pull request for it

5

Iā€™ve spend a bit more time on it, and i was wrong in interpretation on code.
There a still a bug in checkMk, but itā€™s a absolute value

what they do

they calculate a rate for connection_time, express in ms/sec and convert in percent by *10, what is wrong

250ms/sec should be 25%, not 2500% as it calculated now

iā€™ve closed other pull request, and create a new one to fix this

to be able to fix on current version, iā€™ve done a mkp with just the file modified in the path
local/share/check_mk/checks/jolokia_jvm_garbagecollectors

and it will override default one.

1 Like
6

Is this working for you?

I had already tried changing this (I went with / 10 rather than * 0.1) and it seemed to have no impact at all on the metrics reported, neither in the status message nor in the RRD graphs.

7

Yes itā€™s working, iā€™ve to put in
local/share/check_mk/checks/jolokia_jvm_garbagecollectors

restart checkMk.
i use a distributed system, it wouldnā€™t activate by default on all site, iā€™ve to force a activate on all site by editing a user as workaround

8

I had already tried the same thing (apart from using / 10.0 rather than * 0.10) hence my reason for asking, I suspect there may be something wrong with how I deployed this:

First attempt

  1. created a backup of var/check_mk/precompiled_checks/builtin/jolokia_jvm_garbagecollectors in the same dir (jolokia_jvm_garbagecollectors-YYYYMMDD)
  2. edited jolokia_jvm_garbagecollectors to change calculation
  3. removed corresponding file in var/check_mk/precompiled_checks/builtin/

This had no impact - on checking, the ā€œpre-compiledā€ code appears to have been generated rom the backup file rather tha new fileā€¦

Second attempt
As above, but I placed the backup file in /root. However the outcome was the same.

Third attempt
I put a copy of the modified file in local/share/check_mk/checks/, deleted var/check_mk/precompiled_checks/builtin/

This seems to have worked. Is there canonical documentation on how this should be done?

9

The best instance talking about that so far is here:

I do think that there is something more official, but I can not able to find it yet.

10

you donā€™t need to delete the original in var/ā€¦
What you put in local overirde the default checkmk one, it seem to work for quite all plugin i overrided (service now, python and gc_collector)

Otherwise, i mostly read the code for the documentation.

11

This is now fixed in last version

12

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