Optimize MCP query tools for large databases (#826)

The three heaviest MCP tools (get_top_queries_by_cpu, get_top_procedures_by_cpu,
get_query_store_top) timed out on large databases because they scanned every row,
decompressed text on every row, and returned all results for client-side filtering.

Dashboard: add new MCP-specific service methods using multi-phase temp tables —
aggregate numerics first, rank TOP N, then hydrate text via OUTER APPLY for only
the winners. DECOMPRESS now runs on ~N rows instead of the entire table.

Lite: rewrite queries with CTE-based phasing — inner CTE aggregates numeric-only
columns with LIMIT, outer query hydrates text via LEFT JOIN LATERAL for winners.

Both: push database_name filter and TOP N into SQL instead of client-side filtering.
Shared UI methods are untouched.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: erikdarlingdata

Dashboard/Mcp/McpQueryTools.cs

@@ -38,19 +38,13 @@ public static async Task<string> GetTopQueriesByCpu(
             var topError = McpHelpers.ValidateTop(top, "top");
             if (topError != null) return topError;
 
-            var rows = await resolved.Value.Service.GetQueryStatsAsync(hours_back);
+            var rows = await resolved.Value.Service.GetQueryStatsForMcpAsync(hours_back, top, database_name, parallel_only, min_dop);
             if (rows.Count == 0)
             {
                 return "No query stats available for the specified time range.";
             }
 
-            IEnumerable<QueryStatsItem> filtered = rows;
-            if (!string.IsNullOrEmpty(database_name))
-                filtered = filtered.Where(r => string.Equals(r.DatabaseName, database_name, StringComparison.OrdinalIgnoreCase));
-            if (parallel_only || min_dop > 1)
-                filtered = filtered.Where(r => r.MaxDop > 1 && r.MaxDop >= (min_dop > 1 ? min_dop : 2));
-
-            var result = filtered.Take(top).Select(r => new
+            var result = rows.Select(r => new
             {
                 database_name = r.DatabaseName,
                 query_hash = r.QueryHash,
@@ -116,17 +110,13 @@ public static async Task<string> GetTopProceduresByCpu(
             var topError = McpHelpers.ValidateTop(top, "top");
             if (topError != null) return topError;
 
-            var rows = await resolved.Value.Service.GetProcedureStatsAsync(hours_back);
+            var rows = await resolved.Value.Service.GetProcedureStatsForMcpAsync(hours_back, top, database_name);
             if (rows.Count == 0)
             {
                 return "No procedure stats available for the specified time range.";
             }
 
-            IEnumerable<ProcedureStatsItem> filtered = rows;
-            if (!string.IsNullOrEmpty(database_name))
-                filtered = filtered.Where(r => string.Equals(r.DatabaseName, database_name, StringComparison.OrdinalIgnoreCase));
-
-            var result = filtered.Take(top).Select(r => new
+            var result = rows.Select(r => new
             {
                 database_name = r.DatabaseName,
                 full_name = r.FullObjectName,
@@ -187,19 +177,13 @@ public static async Task<string> GetQueryStoreTop(
             var topError = McpHelpers.ValidateTop(top, "top");
             if (topError != null) return topError;
 
-            var rows = await resolved.Value.Service.GetQueryStoreDataAsync(hours_back);
+            var rows = await resolved.Value.Service.GetQueryStoreDataForMcpAsync(hours_back, top, database_name, parallel_only, min_dop);
             if (rows.Count == 0)
             {
                 return "No Query Store data available. Query Store may not be enabled on target databases.";
             }
 
-            IEnumerable<QueryStoreItem> filtered = rows;
-            if (!string.IsNullOrEmpty(database_name))
-                filtered = filtered.Where(r => string.Equals(r.DatabaseName, database_name, StringComparison.OrdinalIgnoreCase));
-            if (parallel_only || min_dop > 1)
-                filtered = filtered.Where(r => r.MaxDop > 1 && r.MaxDop >= (min_dop > 1 ? min_dop : 2));
-
-            var result = filtered.Take(top).Select(r => new
+            var result = rows.Select(r => new
             {
                 database_name = r.DatabaseName,
                 query_id = r.QueryId,