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Cassandra single unreachable node causing total cluster outage


Hello all,

 

Setup:

 

18 Cassandra node cluster. Cassandra version 2.2.8

Amazon C3.2x large machines.

Replication factor of 3 (in 3 different AZs).

Read and Write using Quorum.

 

Use case:

 

  1. Short lived data with heavy updates (I know we are abusing Cassandra here) with gc grace period of 15 minutes (I know it sounds ridiculous). Level-tiered compaction strategy.
  2. Timeseries data, no updates (short lived) (1 hr). TTLed out using Date-tiered compaction strategy.
  3. Timeseries data, no updates (long lived) (7 days). TTLed out using Date-tiered compaction strategy.

 

Overall high read and write throughput (100000/second)

 

Problem:

  1. The EC2 machine becomes unreachable (we reproduced the issue by taking down network card) and the entire cluster becomes unstable for the time until the down node is removed from the cluster. The node is shown as DN node while doing nodetool status. Our understanding was that a single node down in one AZ should not impact other nodes. We are unable to understand why a single node going down is causing entire cluster to become unstable. Is there any open bug around this?
  2. We tried another experiment by killing Cassandra process but in this case we only see a blip in latencies but all the other nodes are still healthy and responsive (as expected).

 

Any thoughts/comments on what could be the issue here?

 

Thanks,
Pratik