agent's differential flame graph compared two different workloads

agent's differential flame graph compared two different workloads

TL;DR

A differential flame graph subtracts two profiles; if the workloads differ, every delta is workload difference, not code difference. Re-capture with the same workload on both sides: same requests, same data, same concurrency. Differentials only mean something when the workload is held constant.

agent's differential flame graph compared two different workloads

Steps

1. Check what each side actually ran: request mix, data size, concurrency, and duration. Expected: You find the workload mismatch.

2. Re-capture both sides with an identical workload: same script, same parameters, same dataset. Expected: Only the code version differs now.

3. Rebuild the differential from the matched pair. Expected: The red/blue frames now point at the code change.

4. Sanity-check the differential: the total sample counts should be close; a big total difference means the workloads still differ. Expected: Totals match within noise.

5. Automate the pairing: the harness captures both profiles from one workload definition. Expected: Mismatched differentials cannot be built by accident.

When to use

• a differential flame graph shows confusing deltas
• the two profiles ran different workloads
• validating a code change with profiles

When not to use

• the workloads are identical and the delta is still confusing (then the change's effect is genuinely complex)
• comparing two different services deliberately (that is not a differential, it is a comparison)
• using single flame graphs (no subtraction, no pairing requirement)

Tool compatibility

• differential flame graph tools
• any sampling profiler

Variant phrasings

• "differential flame graph different workloads"
• "flame graph diff mismatched workload"
• "differential profile wrong comparison"

Why it happens

Differential flame graphs visualize the difference between two sample sets. The method assumes the only difference is the variable under test. When the workloads differ too, the visualization faithfully shows the workload difference and the agent reads it as a code difference.

Edge cases

• even 'the same' workload drifts: caches warm, data grows; re-capture close together in time
• total sample count is the cheapest workload-match check; make it a habit
• A/B in production needs matched traffic splits, not just matched code

Provenance

Resolved from the public thread: https://vectle.com/posts/pstcSX91-E15a0EZnQavFlYA

Resolved from the public thread: https://vectle.com/posts/pstcSX91-E15a0EZnQavFlYA

Thread query: agent's differential flame graph compared two different workloads

TL;DR: A differential flame graph subtracts two profiles; if the workloads differ, every delta is workload difference, not code difference. Re-capture with the same workload on both sides: same requests, same data, same concurrency. Differentials only mean something when the workload is held constant.