perf(db): covering partial index for the reporting measures aggregate

The reporting 'where the money goes' panel joins the latest plan per
property to its recommendations ON plan_id, filters to the default active
set, and sums estimated_cost / counts property_id per measure_type. The
only plan_id index (idx_recommendation_plan_id) is plain, so the aggregate
heap-fetches every recommendation to apply the filter and read those
columns — hundreds of thousands of fetches on large portfolios (434),
which times the panel out.

idx_recommendation_plan_default carries plan_id + measure_type +
property_id + estimated_cost as key columns (drizzle-orm has no INCLUDE),
partial on default = true AND already_installed = false, so the aggregate
runs index-only. Added to the schema and generated via drizzle-kit.

OPS: build CONCURRENTLY out-of-band on prod before the migration runs so it
no-ops there (0258 pattern); the migration uses IF NOT EXISTS for fresh
environments. See the migration file header.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/app/db/migrations/0266_hesitant_bromley.sql

@@ -0,0 +1,21 @@
+-- Covering partial index for the reporting "where the money goes" aggregate.
+-- The query joins the latest plan per property to its recommendations ON
+-- plan_id, filters to default = true AND already_installed = false, and sums
+-- estimated_cost / counts property_id per measure_type. The plain
+-- idx_recommendation_plan_id only locates the rows; the aggregate then
+-- heap-fetches every recommendation to apply the filter and read these
+-- columns, which times out on large portfolios (e.g. 434). Carrying
+-- measure_type, property_id and estimated_cost as key columns makes the whole
+-- aggregate index-only.
+--
+-- OPS: `recommendation` is large, so build this CONCURRENTLY out-of-band on
+-- prod BEFORE this migration runs, so the migration no-ops there (matches the
+-- 0258 idx_plan_recommendations_recommendation_id pattern). A plain
+-- CREATE INDEX here would lock writes on the table. Fresh environments build
+-- it inline via IF NOT EXISTS.
+--
+--   CREATE INDEX CONCURRENTLY IF NOT EXISTS "idx_recommendation_plan_default"
+--     ON "recommendation" USING btree ("plan_id","measure_type","property_id","estimated_cost")
+--     WHERE "default" = true AND "already_installed" = false;
+
+CREATE INDEX IF NOT EXISTS "idx_recommendation_plan_default" ON "recommendation" USING btree ("plan_id","measure_type","property_id","estimated_cost") WHERE "recommendation"."default" = true AND "recommendation"."already_installed" = false;

src/app/db/migrations/meta/_journal.json

@@ -1856,6 +1856,13 @@
       "when": 1783446767021,
       "tag": "0265_uprn_corrections",
       "breakpoints": true
+    },
+    {
+      "idx": 266,
+      "version": "7",
+      "when": 1783511384352,
+      "tag": "0266_hesitant_bromley",
+      "breakpoints": true
     }
   ]
 }

src/app/db/schema/recommendations.ts

@@ -118,6 +118,26 @@ export const recommendation = pgTable(
         sql`${table.default} = true AND ${table.alreadyInstalled} = false`,
       ),
 
+    // Covering partial index for the reporting "where the money goes"
+    // aggregate, which joins the latest plan per property to its
+    // recommendations ON plan_id, filters to the default active set, and sums
+    // estimated_cost / counts property_id per measure_type. The plain
+    // idx_recommendation_plan_id only locates the rows — the aggregate then
+    // heap-fetches every recommendation to apply the filter and read these
+    // columns, which times out on large portfolios. Carrying measure_type,
+    // property_id and estimated_cost as key columns (drizzle-orm has no
+    // INCLUDE) makes the whole aggregate index-only.
+    index("idx_recommendation_plan_default")
+      .on(
+        table.planId,
+        table.measureType,
+        table.propertyId,
+        table.estimatedCost,
+      )
+      .where(
+        sql`${table.default} = true AND ${table.alreadyInstalled} = false`,
+      ),
+
     index("idx_recommendation_material_id").on(table.materialId),
   ],
 );