FASE 7b: DB Performance — Pooling, Stock Summary, N+1 fix

Cambios implementados:

1. Connection pooling (tenant_db.py):
   - psycopg2.pool.ThreadedConnectionPool para master y tenants
   - Wrapper _PooledConnection que devuelve al pool en .close()
   - Cero cambios en blueprints (backward compatible)

2. Tabla inventory_stock_summary + triggers (v3.2):
   - O(1) stock lookup en vez de SUM() sobre historial completo
   - Trigger AFTER INSERT en inventory_operations recalcula stock
   - Poblada inicialmente en ambos tenants
   - Refactor en 6 archivos de servicios para usar la nueva tabla

3. Fix N+1 en process_sale (pos_engine.py):
   - Precarga retail_price en bulk query FOR UPDATE
   - Elimina SELECT individual por item en loop

4. Índices críticos:
   - idx_parts_name_part + pattern_ops (master)
   - idx_inv_ops_inventory_branch_created (tenants)
   - idx_wi_part_stock_positive (master, ya existía desde Fase 1)

Tests: 73/73 pasando (compat + fase3 + fase5 + fase6)
Migración: v3.2_db_performance.sql

pos/services/ai_chat.py

@@ -140,7 +140,7 @@ def get_inventory_context(tenant_conn, branch_id=None):
         cur.execute(f"""
             SELECT COUNT(*) FROM inventory i
             WHERE {where}
-              AND COALESCE((SELECT SUM(quantity) FROM inventory_operations WHERE inventory_id = i.id), 0) <= 3
+              AND COALESCE((SELECT stock FROM inventory_stock_summary WHERE inventory_id = i.id), 0) <= 3
         """, params)
         low_stock = cur.fetchone()[0] or 0
 

pos/services/catalog_service.py

@@ -1411,12 +1411,11 @@ def _get_local_stock_bulk(tenant_conn, branch_id, oem_numbers, catalog_part_ids)
     cur.execute(f"""
         SELECT i.id, i.part_number, i.catalog_part_id,
                i.price_1, i.price_2, i.price_3, i.cost, i.tax_rate,
-               COALESCE(SUM(io.quantity), 0) AS stock,
+               COALESCE(s.stock, 0) AS stock,
                i.image_url
         FROM inventory i
-        LEFT JOIN inventory_operations io ON io.inventory_id = i.id
+        LEFT JOIN inventory_stock_summary s ON s.inventory_id = i.id
         WHERE ({where}) AND i.is_active = true{branch_filter}
-        GROUP BY i.id
     """, params)
 
     result = {}
@@ -1453,13 +1452,12 @@ def _get_local_stock_single(tenant_conn, branch_id, oem_part_number, catalog_par
     cur.execute(f"""
         SELECT i.id, i.price_1, i.price_2, i.price_3, i.cost, i.tax_rate,
                i.location, i.unit, i.barcode,
-               COALESCE(SUM(io.quantity), 0) AS stock,
+               COALESCE(s.stock, 0) AS stock,
                i.image_url
         FROM inventory i
-        LEFT JOIN inventory_operations io ON io.inventory_id = i.id
+        LEFT JOIN inventory_stock_summary s ON s.inventory_id = i.id
         WHERE (i.part_number = %s OR i.catalog_part_id = %s)
           AND i.is_active = true{branch_filter}
-        GROUP BY i.id
         LIMIT 1
     """, params)
 

pos/services/inventory_engine.py

@@ -25,15 +25,33 @@ def _safe_g(attr, default=None):
 def get_stock(conn, inventory_id, branch_id=None):
     """Get current stock for an inventory item. Optionally filter by branch.
 
-    Uses Redis cache first, falls back to PostgreSQL SUM query.
+    Uses Redis cache first, then inventory_stock_summary, falls back to
+    PostgreSQL SUM query.
     """
     # Try Redis first
     cached = get_cached_stock(inventory_id, branch_id)
     if cached is not None:
         return cached
 
-    # Fallback to PostgreSQL
+    # Use inventory_stock_summary (O(1) lookup)
     cur = conn.cursor()
+    if branch_id:
+        cur.execute(
+            "SELECT stock FROM inventory_stock_summary WHERE inventory_id = %s AND branch_id = %s",
+            (inventory_id, branch_id)
+        )
+    else:
+        cur.execute(
+            "SELECT stock FROM inventory_stock_summary WHERE inventory_id = %s",
+            (inventory_id,)
+        )
+    row = cur.fetchone()
+    if row is not None:
+        cur.close()
+        set_cached_stock(inventory_id, row[0], branch_id)
+        return row[0]
+
+    # Fallback to PostgreSQL SUM (legacy, should not reach here if trigger works)
     if branch_id:
         cur.execute(
             "SELECT COALESCE(SUM(quantity), 0) FROM inventory_operations WHERE inventory_id = %s AND branch_id = %s",
@@ -55,21 +73,17 @@ def get_stock(conn, inventory_id, branch_id=None):
 def get_stock_bulk(conn, branch_id=None):
     """Get stock for all items. Returns dict {inventory_id: stock_quantity}.
 
-    Uses PostgreSQL directly (bulk operation, Redis wouldn't help much here
-    unless we pre-populated all keys).
+    Uses inventory_stock_summary for O(1) bulk lookup.
     """
     cur = conn.cursor()
     if branch_id:
         cur.execute("""
-            SELECT inventory_id, COALESCE(SUM(quantity), 0)
-            FROM inventory_operations WHERE branch_id = %s
-            GROUP BY inventory_id
+            SELECT inventory_id, stock
+            FROM inventory_stock_summary WHERE branch_id = %s
         """, (branch_id,))
     else:
         cur.execute("""
-            SELECT inventory_id, COALESCE(SUM(quantity), 0)
-            FROM inventory_operations
-            GROUP BY inventory_id
+            SELECT inventory_id, stock FROM inventory_stock_summary
         """)
     stock_map = {r[0]: r[1] for r in cur.fetchall()}
     cur.close()

pos/services/inventory_vehicle_compat.py

@@ -194,11 +194,7 @@ def get_inventory_by_vehicle(tenant_conn, master_conn, mye_id, branch_id=None):
                i.image_url, i.description, COALESCE(s.stock, 0) as stock
         FROM inventory i
         JOIN inventory_vehicle_compat ivc ON ivc.inventory_id = i.id
-        LEFT JOIN (
-            SELECT inventory_id, SUM(quantity) as stock
-            FROM inventory_operations
-            GROUP BY inventory_id
-        ) s ON s.inventory_id = i.id
+        LEFT JOIN inventory_stock_summary s ON s.inventory_id = i.id
         WHERE ivc.model_year_engine_id = %s {branch_filter}
           AND i.is_active = true
         ORDER BY i.name

pos/services/peer_service.py

@@ -93,11 +93,7 @@ def get_local_inventory(tenant_conn, query: str = None, limit: int = 50) -> list
                COALESCE(s.stock, 0) AS stock,
                i.unit, i.catalog_part_id
         FROM inventory i
-        LEFT JOIN (
-            SELECT inventory_id, SUM(quantity) AS stock
-            FROM inventory_operations
-            GROUP BY inventory_id
-        ) s ON s.inventory_id = i.id
+        LEFT JOIN inventory_stock_summary s ON s.inventory_id = i.id
         WHERE {where}
         ORDER BY i.name
         LIMIT %s

pos/services/pos_engine.py

@@ -224,7 +224,7 @@ def process_sale(conn, sale_data):
     # Lock inventory rows to prevent race conditions on concurrent sales
     cur.execute("""
         SELECT id, part_number, name, cost, price_1, price_2, price_3,
-               tax_rate, branch_id
+               tax_rate, branch_id, retail_price
         FROM inventory
         WHERE id = ANY(%s) AND is_active = true
         ORDER BY id
@@ -327,10 +327,9 @@ def process_sale(conn, sale_data):
     # Create sale items (batch insert) and deduct inventory
     sale_items_data = []
     for item in totals['items']:
-        # Fetch retail_price for savings calculation
-        cur.execute("SELECT retail_price FROM inventory WHERE id = %s", (item['inventory_id'],))
-        rp_row = cur.fetchone()
-        retail_price = rp_row[0] if rp_row else None
+        # retail_price from preloaded bulk query (index 9)
+        inv = inv_rows.get(item['inventory_id'])
+        retail_price = inv[9] if inv else None
 
         sale_items_data.append((
             sale_id, item['inventory_id'], item['part_number'], item['name'],