At MoEngage, the delay between a user action and our ability to react to it is the difference between a conversion and a missed opportunity. Our mission to power real-time customer engagement was hindered by a slow, batch-oriented data pipeline that couldn't keep up with our massive scale. To solve this, we built our "Eventstore" platform on ScyllaDB to handle 250,000 writes per second at 1ms p99 latency to store over 200TB of raw data, architecting a purpose-built schema to tame the challenge of multi-tenancy. This new system guarantees zero data loss through a cross-AZ replication strategy and simplifies cluster management at scale by leveraging ScyllaDB's incremental compaction strategy.