From e7eb3cf64016409ed8a9dfba0c33e22fac8b3ace Mon Sep 17 00:00:00 2001
From: Erik Darling <2136037+erikdarlingdata@users.noreply.github.com>
Date: Wed, 18 Feb 2026 21:32:59 -0500
Subject: [PATCH] Optimize Lite query store collector: CTE + 60-minute window

Restructure the Query Store collection query to avoid nvarchar(max)
query_sql_text in GROUP BY. Aggregation and ranking now happen in a
CTE that only touches sys.query_store_query, query_store_plan, and
query_store_runtime_stats. The expensive join to
sys.query_store_query_text is deferred until after TOP 100 filtering,
dramatically reducing sort memory and I/O.

Also narrows the lookback window from 24 hours to 60 minutes to match
the collection interval and reduce scan volume.

Addresses #134.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 .../RemoteCollectorService.QueryStore.cs      | 75 ++++++++++++-------
 1 file changed, 48 insertions(+), 27 deletions(-)

diff --git a/Lite/Services/RemoteCollectorService.QueryStore.cs b/Lite/Services/RemoteCollectorService.QueryStore.cs
index abde056c..651643a1 100644
--- a/Lite/Services/RemoteCollectorService.QueryStore.cs
+++ b/Lite/Services/RemoteCollectorService.QueryStore.cs
@@ -81,36 +81,57 @@ ORDER BY d.name
 EXECUTE [{dbName.Replace("]", "]]")}].sys.sp_executesql
     N'SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
 
-     SELECT TOP (100)
-         query_id = qsq.query_id,
-         plan_id = qsp.plan_id,
+     ;WITH ranked AS
+     (
+         SELECT TOP (100)
+             query_id = qsq.query_id,
+             plan_id = qsp.plan_id,
+             query_text_id = qsq.query_text_id,
+             query_hash = qsq.query_hash,
+             query_plan_hash = qsp.query_plan_hash,
+             execution_count = SUM(qsrs.count_executions),
+             avg_duration_ms = CONVERT(decimal(18,2), AVG(qsrs.avg_duration) / 1000.0),
+             avg_cpu_time_ms = CONVERT(decimal(18,2), AVG(qsrs.avg_cpu_time) / 1000.0),
+             avg_logical_reads = CONVERT(decimal(18,2), AVG(qsrs.avg_logical_io_reads)),
+             avg_logical_writes = CONVERT(decimal(18,2), AVG(qsrs.avg_logical_io_writes)),
+             avg_physical_reads = CONVERT(decimal(18,2), AVG(qsrs.avg_physical_io_reads)),
+             avg_rowcount = CONVERT(decimal(18,2), AVG(qsrs.avg_rowcount)),
+             last_execution_time = MAX(qsrs.last_execution_time),
+             total_duration = SUM(qsrs.avg_duration * qsrs.count_executions)
+         FROM sys.query_store_query AS qsq
+         JOIN sys.query_store_plan AS qsp
+           ON qsp.query_id = qsq.query_id
+         JOIN sys.query_store_runtime_stats AS qsrs
+           ON qsrs.plan_id = qsp.plan_id
+         WHERE qsrs.last_execution_time >= DATEADD(MINUTE, -60, SYSDATETIME())
+         GROUP BY
+             qsq.query_id,
+             qsp.plan_id,
+             qsq.query_text_id,
+             qsq.query_hash,
+             qsp.query_plan_hash
+         ORDER BY
+             total_duration DESC
+     )
+     SELECT
+         r.query_id,
+         r.plan_id,
          query_text = qst.query_sql_text,
-         query_hash = CONVERT(varchar(64), qsq.query_hash, 1),
-         execution_count = SUM(qsrs.count_executions),
-         avg_duration_ms = CONVERT(decimal(18,2), AVG(qsrs.avg_duration) / 1000.0),
-         avg_cpu_time_ms = CONVERT(decimal(18,2), AVG(qsrs.avg_cpu_time) / 1000.0),
-         avg_logical_reads = CONVERT(decimal(18,2), AVG(qsrs.avg_logical_io_reads)),
-         avg_logical_writes = CONVERT(decimal(18,2), AVG(qsrs.avg_logical_io_writes)),
-         avg_physical_reads = CONVERT(decimal(18,2), AVG(qsrs.avg_physical_io_reads)),
-         avg_rowcount = CONVERT(decimal(18,2), AVG(qsrs.avg_rowcount)),
-         last_execution_time = MAX(qsrs.last_execution_time),
-         query_plan_hash = CONVERT(varchar(64), qsp.query_plan_hash, 1)
-     FROM sys.query_store_query AS qsq
+         query_hash = CONVERT(varchar(64), r.query_hash, 1),
+         r.execution_count,
+         r.avg_duration_ms,
+         r.avg_cpu_time_ms,
+         r.avg_logical_reads,
+         r.avg_logical_writes,
+         r.avg_physical_reads,
+         r.avg_rowcount,
+         r.last_execution_time,
+         query_plan_hash = CONVERT(varchar(64), r.query_plan_hash, 1)
+     FROM ranked AS r
      JOIN sys.query_store_query_text AS qst
-       ON qst.query_text_id = qsq.query_text_id
-     JOIN sys.query_store_plan AS qsp
-       ON qsp.query_id = qsq.query_id
-     JOIN sys.query_store_runtime_stats AS qsrs
-       ON qsrs.plan_id = qsp.plan_id
-     WHERE qsrs.last_execution_time >= DATEADD(HOUR, -24, SYSDATETIME())
-     GROUP BY
-         qsq.query_id,
-         qsp.plan_id,
-         qst.query_sql_text,
-         qsq.query_hash,
-         qsp.query_plan_hash
+       ON qst.query_text_id = r.query_text_id
      ORDER BY
-         SUM(qsrs.avg_duration * qsrs.count_executions) DESC
+         r.total_duration DESC
      OPTION(RECOMPILE);';";
 
                 sqlSw.Start();