Aglet

How to investigate API latency variance with matched traces

An API-variance investigation explains why requests with a comparable contract take different paths or wait different amounts of time. Align matched traces, inspect the first divergent interval, and test one scoped change while preserving response shape, status semantics, and retry safety.

Build a useful investigation brief

  1. Align fast and slow request timelines

    Choose requests with the same route and comparable method, payload shape, result count, and account class. Compare admission wait, application work, queries, locks, dependency calls, serialization, and transfer. Record gaps and sampling limits so a missing span is not described as zero time.

  2. Test the suspected grouping dimension

    Hold route and client action fixed while varying one dimension such as result count, filter, data size, cache state, or dependency response. Compare execution path and duration across several matched cases. Keep values redacted but retain structural fields needed to reproduce the variance.

  3. Evaluate one bounded change

    Try one intervention such as reducing an initial result set, removing redundant work, bounding a query, or changing a dependency wait policy. Replay fast and slow shapes, then check status codes, response fields, ordering, and retry behavior. Do not call reduced work success if required data moved silently elsewhere.

What to carry forward

Deliver a brief with matched traces, grouping dimension, first divergent interval, tested change, and uncertainty about unmeasured work. Investigation is complete when implementation can target one source of variance and verification can compare distributions plus the waiting user action.

Keep the decision with the work.

Use a Work Item in Aglet to record the problem, the evidence you have, and the next decision. Add an owner and priority, then keep updates in the discussion so the next person can follow the reasoning.

Create an account See the product workflow