ClickHouse is interesting - it's also an apache project. I am suprised Uber didn't build AresDB on it. The stigma, unfortunately, of coming from Russia makes it hard for the project to gain mindshare in the Valley.
ClickHouse is licensed under the Apache License 2.0, but isn't an "Apache project" as in an ASF project. Maybe that's what you meant—just want to make that clear for other readers.
ClickHouse scan performance is through the roof, but it also seems fairly difficult to operate compared to the alternatives. For example, the concept of "deep storage" in Druid and Pinot makes rebalancing and replication trivial (at the expense of additional storage space). ClickHouse doesn't have that and requires more babysitting. And that's without even going into something like BigQuery, which is on a completely different level regarding operational simplicity if your use cases support it.
Also, if queries are heavily filtered by arbitrary dimensions, then ClickHouse starts to lose its edge compared to fully-indexed systems.
This makes ClickHouse fairly niche IMO, despite being exceptional at what it does.
We mostly use replicated MergeTree, SummingMergeTree, AggregatedMergeTree etc. And yes, we do use Kafka engine to consume directly from Kafka, in additions to standard Clickhouse inserters.
