Update Jan 2026
We have settled on version 28.0.1 as our target version, for the time being.
This is because this is the last version that officially supports Hadoop 2.
Update: version 27.0.0 is actually the last version that can be built with Hadoop 2 support.
The required option was removed on 28.0.0
Update: version 27.0.0 exhibited some issues with Hadoop 2, even with the custom build profile. Therfore, we have now chosen version 26.0.0 as the target version, for now.
Original description follows.
https://github.com/apache/druid/issues/10462#20-result-caching is a bug fixed in 0.20 that we are seeing in our version, 0.19, namely the whole-query cache on brokers not populated. I was puzzled that Brokers were only registering cache miss, but it seems due to a problem in the code rather in the settings.
Having the Broker query cache working would probably benefit our latency, giving us the possibility to think about using memcached as common broker caching layer (even one host per host would be fine.
