Greetings, We are planning a Cassandra upgrade from 3.7 to 3.11.5 and considering a change to the GC config.
What is the minimum amount of memory that needs to be allocated to heap space when using G1GC? For GC, we currently use CMS. Along with the version upgrade, we'll be running the stateful set of Cassandra pods on new machine types in a new node pool with 12Gi memory per node. Not a lot of memory but an improvement. We may be able to go up to 16Gi memory per node. We'd like to continue using these heap settings: -XX:+UnlockExperimentalVMOptions -XX:+UseCGroupMemoryLimitForHeap -XX:MaxRAMFraction=2 which (if 12Gi per node) would provide 6Gi memory for heap (i.e. half of total available). Here are some details on the environment and configs in the event that something is relevant. Environment: Kubernetes Environment Config: Stateful set of 3 replicas Storage: Persistent Volumes Storage Class: SSD Node OS: Container-Optimized OS Container OS: Ubuntu 16.04.3 LTS Data Centers: 1 Racks: 3 (one per zone) Nodes: 3 Tokens: 4 Replication Factor: 3 Replication Strategy: NetworkTopologyStrategy (all keyspaces) Compaction Strategy: STCS (all tables) Read/Write Requirements: Blend of both Data Load: <1GB per node gc_grace_seconds: default (10 days - all tables) GC Settings: (CMS) -XX:+UseParNewGC -XX:+UseConcMarkSweepGC -XX:+CMSParallelRemarkEnabled -XX:SurvivorRatio=8 -XX:MaxTenuringThreshold=1 -XX:CMSInitiatingOccupancyFraction=75 -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSWaitDuration=30000 -XX:+CMSParallelInitialMarkEnabled -XX:+CMSEdenChunksRecordAlways Any ideas are much appreciated.
