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Cassandra and ElasticSearch would probably have been fine except that Uber dramatically under-provisioned the hardware used for them. The database redundancy was so low that any minor hardware issue could quickly turn into a major outage for all of Uber's monitoring services.

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Well if you’re going to run at RF2 and push them when they can only do 60,000 writes per second vs multiple hundreds of thousands per second with specialized software on the same hardware.

It’s hard to justify using tens of millions of dollars more of hardware more to run Cassandra.

What do you think of ScyllaDB then? Would it have been able to do the job

I think ScyllaDB would have definitely done better than Cassandra (which we were using alongside ElasticSearch), although another thing I mention in this thread is that a lot of existing distributed databases do not have a multi-dimensional inverted index available that can index keys in there primary storage engine.

This makes it tough to use solely either ScyllaDB, ClickHouse or Cassandra for that matter for metrics workloads at scale since they need to find a needle in a haystack - a few thousand time series amongst a set of millions to billions, where users only specify a subset of the dimensions on the metrics in any order they want to. This is hard to do without an inverted index.

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