Metarank

What Metarank is

Metarank is an open-source ranking service for personalized semantic search and recommendations. It uses activity such as clicks and purchases to adjust rankings and personalize results in real time. Its listed capabilities include recommendations, LambdaMART reranking, automatic feature creation and retraining, and serving multiple models for A/B testing. For semantic search and reranking, its documentation describes large language models in bi-encoder and cross-encoder modes. Events can be supplied through Apache Kafka, Apache Pulsar, AWS Kinesis Streams, a REST API, or files; files are supported for import, not inference. Persistence options include local memory, a local directory, Redis, and S3. Metarank runs as a Docker container or JAR on Linux, Windows, and macOS, and its API covers feedback ingestion, model training, ranking, recommendations, LLM inference, and Prometheus metrics. It supports online and offline stores and point-in-time joins. Production guidance recommends Redis persistence; multiple API instances need an external load balancer, since clustering is not provided out of the box.