Plan değişimi P447

(@instance_uuid uniqueidentifier,@window_days int)DELETE r
FROM dbo.agent_job_runs AS r
JOIN dbo.agent_jobs AS j ON j.agent_job_uuid = r.agent_job_uuid
WHERE j.instance_uuid = @instance_uuid
  AND r.run_at < DATEADD(day, -@window_days, SYSUTCDATETIME())

Plan change case #P447 | DB: DB-9 | Regression | Confidence: Medium (review pending)
Query: (@instance_uuid uniqueidentifier,@window_days int)DELETE r FROM dbo.agent_job_runs AS r JOIN dbo.agent_jobs AS j ON j.agent_job_uuid = r.agent_job_uuid WHERE j.instance_uuid = @instance_uuid AND r.run_at < DATEADD(day, -@window_days, SYSUTCDATETIME())
Change: 2026-09-29 09:00 UTC, plan 514 → 546, pattern: Alternating (3 switches)
Impact (Query Store, per execution): duration 2.4 → 460 ms (+18760%); CPU 2.4 → 4 ms (+66%); reads 196 → 236 (+20%); rows 0 → 0
Plan difference: Access only in the old plan: dbo.agent_jobs Index Seek [PK_agent_jobs]; Access only in the new plan: dbo.agent_jobs Index Scan [PK_agent_jobs]; Join only in the old plan: Nested Loops (Inner Join); Join only in the new plan: Merge Join (Inner Join)
Candidate cause: STATS — Statistic dbo.agent_job_runs.CIX_agent_job_runs was updated 2026-09-29 00:46 (sampled 100%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic dbo.agent_job_runs.PK_agent_job_runs was updated 2026-09-29 00:46 (sampled 100%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic dbo.agent_job_runs.IX_agent_job_runs_outcome was updated 2026-09-29 00:01 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic dbo.agent_job_runs.IX_agent_job_runs_window was updated 2026-09-29 00:46 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic dbo.agent_jobs.CIX_agent_jobs was updated 2026-09-29 02:43 (sampled 100%); the plans use this statistic.
Candidate cause: STATS — Statistic dbo.agent_jobs.PK_agent_jobs was updated 2026-09-29 02:43 (sampled 100%); the plans use this statistic.
Candidate cause: PARAM — The two plans alternate in the same period (3 switches): plan choice depends on the parameter value rather than an event (parameter sensitivity).
Counter-evidence: HIGH_VARIANCE — The new plan's duration standard deviation is 877% of the average: the average is not reliable.
Counter-evidence: METADATA_GAP — Metadata collection started on 2026-09-27 and the change was on 2026-09-29: index, statistics and module events could not be evaluated (no data, not no events).
Confidence rationale: Medium: more than one candidate (STATS, PARAM) — competing explanations. Weak counter-evidence: HIGH_VARIANCE, METADATA_GAP.
Note: this is a candidate cause, not proof of the root cause.