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I am running into an issue "me.prettyprint.hector.api.exceptions.HUnavailableException: : May not be enough replicas present to handle consistency level." when I have RF=1, Read Consistency Level = 1 and one of the nodes in 6 node ring/ cluster is down. All of my reads are failing with this exception. Any idea? Ideally only reads that are looking for data in the node which is down should fail and all other reads should be successful?
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In Cassandra it is one of the important aspects for high availability mechanism . It help to Reduce restoration time of a failed node rejoining the cluster and to ensure absolute write availability by tolerating inconsistent reads.
If one of the replicas is down or unreachable, the write operation will fail since Cassandra cannot meet the required consistency level. In this case, Cassandra sacrifices availability to guarantee consistency.
Cassandra, with its distributed architecture, was a natural choice, and by 2013, most of Netflix's data was housed there, and Netflix still uses Cassandra today.
Apple has the biggest Cassandra instance How scalable is Cassandra? In 2014, Apple announced its Cassandra instance had more than 75,000 nodes and stored more than 10 petabytes of data. What's more, a single cluster was over 1,000 nodes.
There could be a few possibilities:
If none of those are the cause, double check that you're specifying the consistency level correctly with Hector and cqlsh.
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