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 real-time
• 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.