Fix Multiple GC declared error when running Druid Cluster

[GWphua]

Description

This problem surfaced when I am attempting to get MM-less Druid running on ZGC with Kubernetes.

After declaring -XX:+UseZGC under JAVA_OPTS for my services, I faced the following error for only the Coordinator, Overlord and Router:
"Error occurred during initialization of VM, Multiple garbage collectors selected".

It turns out that the declaration of the G1GC in the cluster configuration causes the error to surface. I also find it weird that this G1GC configuration is only in the Coordinator/Overlord and Router configuration. By removing the G1GC configuration, I am able to run my cluster with ZGC.

Since G1GC is the default option, there will be no change to Druid's default GC with this removal.

Fixed the multiple GC declared error.

Release note

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Allow Druid to run non-G1 Garbage Collectors with JAVA_OPTS.

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This PR has:

• been self-reviewed.
• been tested in a test Druid cluster.

[kgyrtkirk]

I think the default configs should not set such a thing - unless its really beneficial.
I haven't seen any measurements/etc why this was set initially in the commit logs

Its mentioned in https://druid.apache.org/docs/latest/operations/basic-cluster-tuning/ ; it seems like it was added as a suggestion in this PR.

I looked at -XX flags being set in the files below examples:

• -XX:+ExitOnOutOfMemoryError looks reasonable :)
• -XX:MaxDirectMemorySize seems okay as well
• -XX:+UseG1GC (this)

I agree that the GC algo selection should be removed - as its important to ship something which works out of the box with the least amount of issues.

[kgyrtkirk]

would you like to remove G1GC from other files under examples ?

[GWphua]

@kgyrtkirk Thanks for the quick reply. I have removed the declaration in all files under examples.

[kgyrtkirk]

note: there is no need to force push the branch as merge will be done with a squash (don't rebase your downstream branch)

[kgyrtkirk]

lol :)

[GWphua]

hi @kgyrtkirk

Thanks for approving my PR, can I trouble you to merge this PR now that the CI has passed? 😄

[kgyrtkirk]

Thank you @GWphua for fixing this!