Plan değişimi P439

(@condition nvarchar(4000),@incTest bit,@types1 nvarchar(4000),@sid int,@dbName nvarchar(4000),@tag nvarchar(4000),@top int)SELECT TOP (@top) c.ChunkId, c.DocId, d.SourceType, d.SourceRef, d.Title, c.Heading, c.Text, CAST(ft.[RANK] AS float) AS Score
FROM CONTAINSTABLE(rag.Chunk, Text, @condition) AS ft
JOIN rag.Chunk AS c ON c.ChunkId = ft.[KEY]
JOIN rag.Document AS d ON d.DocId = c.DocId
WHERE (d.IsActive = 1 OR (@incTest = 1 AND d.ExclusionReason = 'TestDb')) AND d.SourceType IN (@types1)
AND (@sid IS NULL OR d.ServerID = @sid) AND (@dbName IS NULL OR d.DatabaseName = @dbName)
AND (@tag IS NULL OR EXISTS (SELECT 1 FROM STRING_SPLIT(d.Tags, ',') AS t WHERE LTRIM(RTRIM(t.value)) = @tag))
ORDER BY ft.[RANK] DESC, c.ChunkId

Plan change case #P439 | DB: DB-11 | Regression | Confidence: Low (review pending)
Query: (@condition nvarchar(?),@incTest bit,@types1 nvarchar(?),@sid int,@dbName nvarchar(?),@tag nvarchar(?),@top int)SELECT TOP (@top) c.ChunkId, c.DocId, d.SourceType, d.SourceRef, d.Title, c.Heading, c.Text, CAST(ft.[RANK] AS float) AS Score FROM CONTAINSTABLE(rag.Chunk, Text, @condition) AS ft JOIN rag.Chunk AS c ON c.ChunkId = ft.[KEY] JOIN rag.Document AS d ON d.DocId = c.DocId WHERE (d.IsActive = ? OR (@incTest = ? AND d.ExclusionReason = ?)) AND d.SourceType IN (@types1) AND (@sid IS NULL OR d.ServerID = @sid) AND (@dbName IS NULL OR d.DatabaseName = @dbName) AND (@tag IS NULL OR EXISTS (SELECT ? FROM STRING_SPLIT(d.Tags, ?) AS t WHERE LTRIM(RTRIM(t.value)) = @tag)) ORDER BY ft.[RANK] DESC, c.ChunkId
Change: 2026-10-06 16:00 UTC, plan 64741 → 64743, pattern: Transition
Impact (Query Store, per execution): duration 8.9 → 44.5 ms (+401%); CPU 8.7 → 44.3 ms (+412%); reads 2,967 → 24,504 (+726%); rows 2.51 → 16.04 (+539%)
Plan difference: no operator-level difference
Candidate cause: STATS — Statistic rag.Chunk.PK_Chunk was updated 2026-10-05 22:47 (sampled 47.4%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Chunk.UQ_Chunk_DocSeq was updated 2026-10-05 22:47 (sampled 50.7%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Chunk._WA_Sys_00000003_49309088 was updated 2026-10-05 22:47 (sampled 47.4%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Document.PK_Document was updated 2026-10-06 01:16 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Document.UQ_Document_Source was updated 2026-10-06 04:00 (sampled 100%); 3 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Document._WA_Sys_0000000A_428392F9 was updated 2026-10-05 22:57 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Document._WA_Sys_00000005_428392F9 was updated 2026-10-05 22:46 (sampled 100%); 2 updates in the window; the plans use this statistic.
Candidate cause: STATS — Statistic rag.Document._WA_Sys_0000000E_428392F9 was updated 2026-10-06 05:48 (sampled 100%); 3 updates in the window; the plans use this statistic.
Candidate cause: WORKLOAD — The plans see a different workload: rows per execution 2.51 → 16.04. The plans may have been compiled for different parameters or batch sizes.
Counter-evidence: WORK_PROPORTIONAL — Rows per execution changed 6.39× and duration 5.01×; duration per row 3.5316 → 2.7713 ms: the duration difference comes from the amount of data processed, not the plan.
Counter-evidence: HIGH_VARIANCE — The old plan's duration standard deviation is 127% of the average: the average is not reliable.
Counter-evidence: SAME_SHAPE — The two plans have the same operator tree (operators, tables, indexes): the plan did not change; the difference is only in the compiled parameter values and row estimates. The slowness may come from the amount of data this parameter value processes or from waits, not from plan choice.
Confidence rationale: Low: strong counter-evidence (WORK_PROPORTIONAL, SAME_SHAPE).
Note: this is a candidate cause, not proof of the root cause.