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From Nate McCall <>
Subject Re: OOM after a while during compacting
Date Thu, 05 Apr 2018 21:52:13 GMT
> - Heap size is set to 8GB
> - Using G1GC
> - I tried moving the memtable out of the heap. It helped but I still got
> an OOM last night
> - Concurrent compactors is set to 1 but it still happens and also tried
> setting throughput between 16 and 128, no changes.

That heap size is way to small for G1GC. Switch back to the defaults with
CMS. IME, G1 needs > 20g for *just* the JVM to see improvements (but this
also depends on workload and a few other factors). Stick with the CMS
defaults unless you have some evidence-based experiment to try.

Also worth noting that with a 1TB gp2 EBS volume, you only have 3k IOPS to
play with before you are subject to rate limiting. If you allocate a volume
greater than 3.33TB, you get 10K IOPS and the rate limiting goes away (you
can see this playing around with the EBS sizing in the AWS calculator: Another common mistake here
is accidentally putting the commitlog on the boot volume which has a super
low amount of IOPS given it's 64g (?iirc) by default.

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