- Cassandra: 12 (2*6) node i3.xlarge AWS instance (4 cpu cores, 30GB ram) running cassandra trunk off of jasobrown/14503 jdd7ec5a2 (Jasons patched internode messaging branch) vs the same footprint running 3.0.17
- Two datacenters with 100ms latency between them
- No compression, encryption, or coalescing turned on
ndbench sent 1.5k QPS at a coordinator level to one datacenter (RF=3*2 = 6 so 3k global replica QPS) of 4kb single partition BATCH mutations at LOCAL_ONE. This represents about 250 QPS per coordinator in the first datacenter or 60 QPS per core. The goal was to observe P99 write and read latencies under various QPS.
The good news is since the
CASSANDRA-14503 changes, instead of keeping the mutations on heap we put the message into hints instead and don't run out of memory. The bad news is that the MessagingService-NettyOutbound-Thread's would occasionally enter a degraded state where they would just spin on a core. I've attached flame graphs showing the CPU state as Jason Brown applied fixes to the OutboundMessagingConnection class.
Jason Brown has committed a number of fixes onto his jasobrown/14503-collab branch including:
1. Limiting the amount of time spent dequeuing messages if they are expired (previously if messages entered the queue faster than we could dequeue them we'd just inifinte loop on the consumer side)
2. Don't call dequeueMessages from within dequeueMessages created callbacks.
We're continuing to use CPU flamegraphs to figure out where we're looping and fixing bugs as we find them.