Front-end observability at scale: How OpenReplay captures billions of daily events in real time with ClickHouse

OpenReplay is an open-source, self-hosted session replay and product analytics platform that enables developers and product teams to observe user interactions, diagnose bugs, and analyze behavior while preserving customers’ control over their data. After encountering slow queries, difficult sharding, poor compression, and labor-intensive retention cleanup in Postgres, the company migrated behavioral-event storage and analytics to ClickHouse, while retaining Postgres for metadata. ClickHouse improved session-search performance to roughly one second, dramatically reduced storage requirements, and automated data retention through TTL policies, eliminating disruptive manual cleanup work. OpenReplay uses a centralized ClickHouse pipeline in which behavioral events enter a flat events table and materialized views transform them into downstream datasets, shortening pipeline changes and supporting rapid feature experimentation. Native JSON support also enables customers to define and query custom analytics events for funnels, heat maps, and flows. Large customer deployments ingest billions of events and up to roughly 6 TB daily on a single vertically scaled ClickHouse instance, an approach designed to minimize operational overhead in self-hosted environments. The company also uses query caching to accelerate repeated analytics requests and is extending ClickHouse to support AI agents that review session recordings and identify issues proactively.

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