Hi there,
after upgrading from 2.1 to 2.2.13, Cassandra eats up all available memory 
within one week. The following is a diagram of the left available RAM of a 
single node over the course of a week:
https://imgur.com/a/H9BDBxC <https://imgur.com/a/H9BDBxC>

Nodes are bare metal, 12 cores with 64GB RAM each, swapping disabled and 
configured with row cache disabled and auto sized key cache. Jemalloc is not 
configured.

This is the same for all nodes. There is no noticeable cpu load on these nodes, 
disk io is also fine, just as tpstats. Heap dumps look fine and if you check 
memory usage via JMX everything seems to be in order also (max heap 8GB, heap 
memory usage goes down to 1GB after GC)

The memory usage reported by top (res) is always around 20GB for the cassandra 
process which also seems to high for us (heap + off heap) as the offheap memory 
allocated by DirectByteBuffers is only around 400MB (reported by jxray).

The available system memory slowly degrades all the time without any other 
memory intensive processes running. We currently drain and restart our nodes, 
if the available memory sinks below 5GB. That means that after a week, there is 
an offset of around 40GB between the reported memory usage of cassandra and the 
real memory usage.

If we stop cassandra, nearly 100% of the system memory is available again.

Has anybody observed similar memory usage with 2.2?

If so, how to measure cassandras real memory usage if top and other system 
tools are way off?

Do you know if this problem has been solved with 3.11?

Cheers,
Matthias

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