Druid historicals caching for queries

Configuration reference · Apache Druid

druid.cache.sizeInBytes The maximum size of the cache in bytes on heap. It can be configured as described in here. min(1GiB, Runtime.maxMemory / 10)

Why does cache size is limited to 1GB when machine heap size can be increased to 128GB(for r5 4x large) machines. We have static data stored in druid served for queries. what is recommendation memory size for local caching. we do use caffeine for local caching.

That is just the default. You can configure it as needed for your workload.