dianping/cat

CAT is a real-time application monitoring platform originally built by Meituan-Dianping (a major Chinese tech company). It solves the problem of knowing what's happening inside your software systems right now, tracking errors, slow requests, and performance metrics across all your services as they occur, not after the fact. The way it works: small client libraries embedded in your application code send monitoring data (transactions, events, heartbeats, metrics) to a central CAT server, which processes everything in near-real-time and displays dashboards and alerts. Because data processing completes within seconds of generation, your engineering team can spot and respond to problems almost immediately rather than discovering them from user complaints. CAT is designed for large-scale distributed systems, multiple services spread across many servers, and includes a high-availability setup to ensure the monitoring system itself doesn't become a point of failure. Client libraries are available for Java, C, C++, Python, Go, and Node.js, so teams with mixed technology stacks can use a single monitoring platform. You would use this if you're running backend services and need real-time visibility into performance, error rates, and system health. The server is written in Java and stores log data in HDFS (Hadoop's distributed file system).