Key takeaways
- A latency figure without a path, sample size, date and percentile distribution is marketing, not measurement.
- Averages hide exactly the behaviour that matters; p99 and p99.9 are where traders actually feel a platform.
- Ask what is excluded from the measurement — that is usually where the interesting latency lives.
Define the path before the number
'Latency' is meaningless without endpoints. Order acknowledgement from the edge? Matching engine internal processing? Trader click to visible fill? These can differ by orders of magnitude, and vendors naturally quote the flattering one.
A credible figure states both endpoints explicitly, and ideally reports several paths so the reader can see where time is actually spent.
Report distributions, not averages
An average latency of 5ms is compatible with a meaningful share of requests taking 500ms. Traders do not experience the average; they experience the bad tail, and they experience it at exactly the busiest moments.
Report p50, p95, p99 and p99.9 together with the sample size and the observation window. If a vendor reports only a single number, ask which percentile it is — the answer is often 'the average', and sometimes 'the best'.
What a credible latency claim states
| Element | Why it matters |
|---|---|
| Measured path (both endpoints) | Determines what is actually being timed |
| Percentiles p50/p95/p99/p99.9 | Averages conceal the tail traders feel |
| Sample size and window | A good minute is not a claim about a platform |
| Geography and network path | Client-observed latency depends heavily on both |
| Load conditions | Quiet-period figures do not describe a market open |
| Date measured | Infrastructure changes; a year-old figure describes a different system |
| What is excluded | Queueing and backlog are often quietly outside the measurement |
Backlog and failures belong in the report
A system can post excellent latency while dropping or deferring work. Any honest report includes the failure rate and any backlog during the measurement window, because a fast path that sheds load is not fast — it is incomplete.
This is also why a live 'latency ticker' on a marketing site is usually decorative. Unless it states path, sample, percentiles and methodology alongside the number, it is an animation. There is no evidence that publishing one improves search performance, and a number nobody can interpret does not build trust with technical buyers.