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I have recently upgraded our Cassandra cluster from 3.11 to 4.0 with the long term goal to also upgrade the Java version. I did not want to do both of these things at once for obvious reasons, however we have been upgraded on C4 for just over two weeks now and I'm looking to upgrade the Java version from jdk8 to jdk11, and also move from CMS Garbage Collector to G1GC.

We wanted to get an idea of what the impact of moving to G1GC would be before going big bang across all nodes.

Is it safe to use a different Garbage collector on different nodes? or should this be something setup in a test environment to monitor?

Thanks in advance.

Olaf Kock
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guyver4mk
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2 Answers2

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Yes! That is actually the recommended practice when changing/testing new GC types, assuming that you cannot fully simulate production workloads in a lower environment.

I'd advise making the switch on one or two nodes, and then monitor their performance relative to the CMS nodes.

Aaron
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    This is what I was thinking, as it would be difficult to replicate the type of traffic which we produce on the production environment, without switching over to the test cluster to test it, which would not be an optimal practice. Thank you. – guyver4mk Nov 10 '21 at 12:47
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Logically you can do it since they are different java processes running on different machines. Actual intention behind you doing this activity is to test you must analyze the impact on test environment first and then apply changes on production if you find test results suitable.

Manish Khandelwal
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    I understand this from a general use point of view. However it would be difficult to replicate the throughput of the production traffic which we generate based on the type of workload it handles. So any test done in a separate environment would possibly either generate a skewed view of the GC cycle, or worse, show a drastic improvement on an incorrect workload suggesting a switch in production would be beneficial.... If that makes sense. – guyver4mk Nov 10 '21 at 12:52