Monday, August 5, 2019

Cassandra: when to add capacity?



How does one know when it's time to add capacity to a cassandra cluster? Error msgs? Performance? Some other tell-tale sign?



Since capacity planning with Cassandra is a (seemingly) black art knowing where to start and when to grow could be somewhat problematic.



Answer



Without knowing anything about your workload, I'd start looking at:




  • IO queue length

  • CPU load

  • Amount of data read vs written

  • GC behavior

  • Compaction stats




When any of these start to get "high" (definition depends on your hardware) then it's time to revisit your application, or scale up.


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