latencyconsistency

Latencyconsistency, sometimes written latency consistency, is a property of a system describing the stability of end-to-end latencies across requests and over time. It measures how predictable delays are, not just how small they are on average. High latency consistency means most requests experience similar delays, while low consistency shows wide variation or jitter.

Metrics and measurement: Common metrics include p95 and p99 latency, median latency, mean latency, standard deviation, interquartile range, and coefficient of variation. Jitter is a related concept describing latency variation between successive requests. In distributed systems, latency distributions can be analyzed per client, region, or globally, often using cumulative distribution functions.

Causes: Network congestion, queueing delays, server load, garbage collection pauses, context switches, route changes, and hardware heterogeneity can reduce consistency. Bursty traffic and multi-tenant interference also contribute to variability.

Implications: In interactive applications such as online gaming, dashboards, or financial trading, latency consistency improves user experience and predictability of control. In deadline-driven systems, tail latency (e.g., p99) is often more important than average latency.

Techniques to improve: Capacity planning and overprovisioning; quality of service and traffic shaping; pacing and smoothing of request streams; deterministic networking approaches; caching and content delivery optimizations; prefetching and warm pools; fast paths for hot requests; CPU isolation and real-time scheduling; minimizing long GC pauses and other slow components.

Trade-offs: Improving consistency can trade off some average latency or throughput and may increase cost or system complexity. Effective measurement requires instrumentation that captures synchronized latency data across components to accurately reflect variability.

Related concepts: latency, jitter, quality of service, deterministic networking, and tail latency in distributed systems.