# Latency Latency is the most critical performance metric for realtime messaging platforms. That doesn't mean just hitting a one-off figure to advertise. It's about providing **consistently low latencies** to all regions, for all use cases, all the time. Ably's platform achieves this by providing the lowest latencies of any Pub/Sub WebSockets platform, with a **global median latency of 37ms**. Understand how Ably optimizes its transit latency to consistently provide your users with the best possible realtime experience. ## Why latency matters In realtime applications, latency directly impacts user experience and application responsiveness. Whether it's live chat, collaborative editing, multiplayer gaming, or financial trading, your users expect near-instantaneous message delivery. Even a small increase in latency can significantly degrade the perceived quality of your application. ## Latency metrics Ably measures and optimizes for two latency metrics to ensure consistent performance across the platform: ### Round-trip latency Round-trip latency measures the total time it takes for a message to travel from a publisher, through Ably's infrastructure, to a subscriber, and back again. #### Round-trip latency - Last 7 days ### Message delivery latency Message delivery latency measures the time taken from when a message is published to Ably until it is delivered to a subscriber. This metric focuses on the core messaging performance without including the return path. #### Message delivery - Median latency - Last 7 days #### Message delivery - P90 latency - Last 7 days ## How latency is measured Ably employs rigorous measurement methodologies to ensure latency performance is accurately captured across its global platform. Latency measurements are taken continuously at the following rates: * 70 measurements per second. * 4,200 measurements per minute. * 252,000 measurements per hour. * 6,048,000 measurements per day. ### Round-trip latency measurement Round-trip latency is measured using real browser monitoring through Uptrends Real Browser Monitoring. This approach provides: * **Real browser simulation**: Measurements are conducted using actual browser instances, ensuring realistic network conditions. * **Global coverage**: Monitoring points are distributed across the globe using a third party service. * **Pub/sub simulation**: Real browsers publish messages and measure the complete round-trip time. * **Continuous monitoring**: Measurements are conducted continuously to capture performance across different time periods and load conditions. This methodology ensures that round-trip latency measurements reflect the actual experience of end-users accessing Ably through web browsers. ### Message delivery latency measurement Message delivery latency is measured using Ably's internal quality of service (QOS) application. The measurement process includes: * **Continuous message publishing**: Messages are sent continuously to a common Ably channel at a rate of 5 messages per second, per region. * **Payload inclusion**: Each message contains a payload with region information and precise publish timestamp. * **Delivery tracking**: Subscribers across different regions receive and timestamp the messages. * **Latency calculation**: Delivery latency is calculated by subtracting the publish timestamp from the delivery timestamp. * **Statistical sampling**: The 5 messages per second rate ensures statistically relevant sample sizes across all regions. This methodology provides comprehensive coverage of Ably's global infrastructure and ensures that latency measurements reflect real-world conditions across all datacenters and regions. ### Measurement infrastructure Both measurement systems operate continuously to provide realtime insights into Ably's latency performance. They include: * **Automated collection**: Measurements are collected automatically without manual intervention * **Realtime analysis**: Latency data is processed and analyzed in realtime * **Alerting**: Performance thresholds trigger alerts when latency exceeds targets * **Historical tracking**: Long-term trends are maintained for performance optimization ### Statistical analysis Latency data is analyzed across multiple percentiles to ensure comprehensive performance reporting: * **P50 (median)**: Represents typical performance under normal conditions. * **P90**: Ensures 90% of messages meet performance targets. This multi-percentile approach ensures that Ably's latency performance is consistent and predictable across all load conditions.