# Capacity causal ordering

<!-- auto-oncall-optimization-record
{
  "schemaVersion": "auto-oncall-optimization-record-v1",
  "optimizationId": "capacity-causal-ordering-2026-08-06",
  "problems": [
    {
      "problemId": "capacity-signal-ranked-ahead-of-better-workload-mechanism",
      "summary": "A capacity scenario paragraph ordering capacity changes against downstream TopSQL, GC, hotspot, and IO signals was tested on false-capacity and true-capacity cases. The baseline already produced the same ordering, so the paragraph produced no material target improvement and was reverted.",
      "status": "ineffective",
      "issueKeys": ["TCID-12926", "TCID-12985", "ST-2864", "APID-29277"],
      "sourceRefs": [
        "https://tidb.atlassian.net/browse/TCID-12926#problem:scale-in-overlap-does-not-prove-capacity-root-cause",
        "https://tidb.atlassian.net/browse/TCID-12985#problem:available-rcu-does-not-explain-latency"
      ],
      "signalTextIncludesAny": [
        "capacity alert promoted over workload mechanism",
        "scale in overlap treated as direct cause",
        "quota treated as limiting despite negligible resource control wait"
      ],
      "observedThrough": "2026-08-06",
      "effectiveAt": null,
      "verifiedAt": "2026-08-06T13:52:00+08:00",
      "attemptedAction": "Add a capacity-resource-pressure paragraph that ranks the first effective capacity change against downstream workload, hotspot, GC, and IO signals.",
      "evidenceUrl": null
    }
  ]
}
-->

- Owner: auto-oncall-services
- Implementation status: evaluated locally and reverted; not deployed
- Effective status: `ineffective`

## Verification

Single-variable A/B on two targets and two controls changed no causal status,
primary mechanism, uncertainty boundary, or action. True disk-headroom controls
remained capacity cases while scale-in and RCU targets remained bounded.

## Next action

Do not repeat this paragraph-only action unless new evidence shows the existing
quota, saturation, wait-path, and workload checks ordering causes incorrectly.