Doesn't matter all that much. For ingestion, you might have one VM running one Java process and one DB process as a microservice (I like Dropwizard and PostgreS

Doesn't matter all that much. For ingestion, you might have one VM running one Java process and one DB process as a microservice (I like Dropwizard and PostgreSQL for this). The worker itself would be another Java process with a 100 thread max thread pool that either periodically checks for new work, or uses the new NOTIFY semantics new to Postgres 9.6. In this case the "secret sauce" is that the worker has some extra smarts to reorder the queue to avoid resource hogs, which is the cool part.