Apache Druid vs Apache Flink

Apache Druid is a free, open-source analytics database for querying streaming and batch data. It is designed to return OLAP queries in milliseconds, including on high-cardinality datasets with billions to trillions of rows. The project describes applications ranging from hundreds to 100,000 queries per second. Native Apache Kafka and Amazon Kinesis integrations support low-latency ingestion and querying as data arrives. Druid organizes ingested data into columnar, time-indexed, encoded and compressed storage. Queries can use Druid SQL or JSON-over-HTTP, and joins are available during ingestion or at query time. Its web console can load data, manage datasources and tasks, show server status and run queries. Extensions connect to storage, databases and formats including S3, HDFS, Azure, PostgreSQL, Avro, ORC and Parquet. Druid can be self-hosted on Linux, macOS and other Unix-like systems; Windows is not supported. The local quickstart needs at least 6 GiB of RAM and Java 17. Production security controls require configuration.

Apache Flink is a free, self-hosted framework and distributed processing engine for stateful computations over unbounded and bounded data streams. It supports event-driven applications, stream and batch analytics, and data pipelines and ETL. Listed correctness features include exactly-once state consistency, event-time processing and late-data handling. APIs include SQL for stream and batch data, DataStream and ProcessFunction for time and state. Operational capabilities cover flexible deployment, high availability, savepoints, scale-out architecture, very large state and incremental checkpoints. The project lists low latency, high throughput and in-memory computing. Flink runs in common cluster environments; for Kubernetes, the Kubernetes Operator is identified as the standard deployment mechanism. Connectors include AWS, Cassandra, Elasticsearch, Google Cloud PubSub, HBase, Hive, JDBC, Kafka, MongoDB, OpenSearch, Prometheus, Pulsar and RabbitMQ. Security requires configuration because SSL/TLS, REST authentication and SQL Gateway authentication are disabled by default. It is available at free under Apache License v2.