Plan değişimi P421

(@condition nvarchar(4000),@incTest bit,@types1 nvarchar(4000),@sid int,@dbName 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)
ORDER BY ft.[RANK] DESC, c.ChunkId

Plan change case #P421 | DB: DB-11 | Regression | Confidence: Medium (review pending)
Query: (@condition nvarchar(?),@incTest bit,@types1 nvarchar(?),@sid int,@dbName 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) ORDER BY ft.[RANK] DESC, c.ChunkId
Change: 2026-10-06 15:00 UTC, plan 37017 → 64735, pattern: Transition
Impact (Query Store, per execution): duration 23.5 → 52.4 ms (+123%); CPU 23.4 → 52.3 ms (+123%); reads 21,439 → 46,108 (+115%); rows 17.43 → 13.14 (-25%)
Plan difference: Access only in the old plan: rag.Chunk Clustered Index Seek [PK_Chunk]; rag.Document Clustered Index Seek [PK_Document]; Access only in the new plan: rag.Document Index Scan [UQ_Document_Source]; rag.Document Clustered Index Seek [PK_Document] (lookup); rag.Chunk Index Seek [UQ_Chunk_DocSeq]; rag.Chunk Clustered Index Seek [PK_Chunk] (lookup); Join only in the old plan: Nested Loops (Inner Join) ×2; Join only in the new plan: Hash Match (Inner Join); Nested Loops (Inner Join) ×3
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: GROWTH — From the old plan's period to the change, rag.Document rows changed +5% and size +22% (2026-10-04 → 2026-10-06).
Counter-evidence: HIGH_VARIANCE — The new plan's duration standard deviation is 104% of the average: the average is not reliable.
Confidence rationale: Medium: more than one candidate (STATS, GROWTH) — competing explanations. Weak counter-evidence: HIGH_VARIANCE.
Note: this is a candidate cause, not proof of the root cause.