Plan değişimi P480

(@MaxAttempts int,@BatchSize int,@LeaseSeconds int)WITH c AS (
        SELECT TOP (@BatchSize) *
        FROM rag.EmbedQueue WITH (READPAST, UPDLOCK, ROWLOCK)
        WHERE Status = 'Queued' OR (Status = 'Running' AND LeaseUntilUtc < DBA.fn_Now() AND Attempt < @MaxAttempts)
        -- Vaka/KB önce: bekçi her gün binlerce profili kuyruğa alır, onaydan sonra gelen vaka onların ardında beklemesin
        ORDER BY CASE SourceType WHEN 'Profile' THEN 1 ELSE 0 END, QueueID
    )
    UPDATE c SET Status = 'Running', Attempt = Attempt + 1, LeaseUntilUtc = DATEADD(second, @LeaseSeconds, DBA.fn_Now())
    OUTPUT inserted.QueueID, inserted.SourceType, inserted.SourceRef, inserted.Attempt

Plan change case #P480 | DB: DB-11 | Regression | Confidence: Medium (review pending)
Query: (@MaxAttempts int,@BatchSize int,@LeaseSeconds int)WITH c AS ( SELECT TOP (@BatchSize) * FROM rag.EmbedQueue WITH (READPAST, UPDLOCK, ROWLOCK) WHERE Status = ? OR (Status = ? AND LeaseUntilUtc < DBA.fn_Now() AND Attempt < @MaxAttempts) ORDER BY CASE SourceType WHEN ? THEN ? ELSE ? END, QueueID ) UPDATE c SET Status = ?, Attempt = Attempt + ?, LeaseUntilUtc = DATEADD(second, @LeaseSeconds, DBA.fn_Now()) OUTPUT inserted.QueueID, inserted.SourceType, inserted.SourceRef, inserted.Attempt
Change: 2026-10-05 09:00 UTC, plan 45488 → 46765, pattern: Alternating (4 switches)
Impact (Query Store, per execution): duration 0.6 → 15.4 ms (+2286%); CPU 0.6 → 15.3 ms (+2285%); reads 25 → 990 (+3885%); rows 1 → 7.86 (+686%)
Plan difference: Access only in the old plan: rag.EmbedQueue Table Update; rag.EmbedQueue Table Scan; Access only in the new plan: rag.EmbedQueue Index Update [UX_EmbedQueue_Pending]; rag.EmbedQueue Clustered Index Update [PK_EmbedQueue]; rag.EmbedQueue Clustered Index Scan [PK_EmbedQueue]; Warning only in the new plan: UnmatchedIndexes; Estimated cost: 0.038 → 0.777; estimated rows: 1 → 100
Candidate cause: STATS — Statistic rag.EmbedQueue.PK_EmbedQueue was updated 2026-10-04 09:05 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.EmbedQueue.IX_EmbedQueue_Status was updated 2026-10-04 08:37 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.EmbedQueue.UX_EmbedQueue_Pending was updated 2026-10-04 08:16 (sampled 100%); the plans use this statistic.
Candidate cause: STATS — Statistic rag.EmbedQueue._WA_Sys_00000005_50D1B250 was updated 2026-10-05 07:50 (sampled 100%); 4 updates in the window; the plans use this statistic.
Candidate cause: WORKLOAD — The plans see a different workload: rows per execution 1 → 7.86. The plans may have been compiled for different parameters or batch sizes.
Candidate cause: PARAM — The two plans alternate in the same period (4 switches): plan choice depends on the parameter value rather than an event (parameter sensitivity).
Counter-evidence: LOW_SAMPLE — The old plan ran only 27 times: the sample is small and the average is weak.
Confidence rationale: Medium: more than one candidate (STATS, WORKLOAD + PARAM) — competing explanations. Weak counter-evidence: LOW_SAMPLE.
Note: this is a candidate cause, not proof of the root cause.