Latency & SRE Glossary
Explore 13 platform engineering definitions related to Latency & SRE.
Latency budget
Total time allocated for a complete user-facing request across all architectural hops.
SLA and SLO (service level agreement vs objective)
SLA is a contract with guarantees; SLO is the internal target set stricter than SLA to create error budget.
p50 latency (median)
50th percentile of request durations: half of requests complete faster, half slower.
p99 latency
99th percentile of request durations: captures experience of users under stress.
Headroom (latency)
Gap between measured latency and SLA ceiling; buffer for unpredictable spikes.
Cold start (serverless)
Extra latency when serverless function starts on new execution environment.
Cross-AZ latency
Round-trip time between availability zones; adds cost and latency to replication.
Tail latency
High-percentile latency values (p99, p99.9) representing slowest requests.
Fan-out (distributed systems)
Single request triggers multiple parallel downstream calls.
N+1 query problem
One query to fetch list plus N queries for each item; causes database round-trips.
Speed of light in optical fibre
~200,000 km/s; physical lower bound on network latency regardless of optimization.
Thundering herd
Many clients simultaneously access resource that just became available.
Percentile latency (p50 / p99 / p999)
Statistical measure of request duration distribution.