This document discusses high-throughput transactional stream processing on HBase using Continuuity Reactor. Continuuity Reactor is a platform built on Hadoop and HBase that allows collecting, processing, storing and querying data with ACID guarantees using a flow-based programming model. Flows in Reactor are composed of flowlets connected by queues, with all processing occurring within transactions for consistency. The document outlines how Reactor implements transactions using an optimistic concurrency control approach based on multi-version concurrency control and HBase timestamps. It also discusses queue design and optimizations for performance.