perf: connection pooling, query consolidation, inline chart data, batch milestones

app/routes/api.py

@@ -44,18 +44,24 @@ def progress_over_time():
 
     where_sql = " AND ".join(where_clauses)
 
+    # Use CTE for first_weight instead of correlated subquery
     rows = query(f"""
+        WITH first_weights AS (
+            SELECT DISTINCT ON (user_id) user_id, weight_kg AS first_weight
+            FROM checkins
+            ORDER BY user_id, checked_in_at ASC
+        )
         SELECT
             u.id                    AS user_id,
             u.display_name,
             u.username,
             u.starting_weight_kg,
-            (SELECT weight_kg FROM checkins
-             WHERE user_id = u.id ORDER BY checked_in_at ASC LIMIT 1) AS first_weight,
+            fw.first_weight,
             c.weight_kg,
             c.checked_in_at
         FROM checkins c
         JOIN users u ON u.id = c.user_id
+        LEFT JOIN first_weights fw ON fw.user_id = u.id
         WHERE {where_sql}
         ORDER BY u.id, c.checked_in_at ASC
     """, params)
@@ -144,17 +150,26 @@ def chart_data(user_id):
 @login_required
 def comparison():
     """Return all-user comparison data for bar charts."""
+    # Use CTE with window functions instead of correlated subqueries
     users = query("""
+        WITH user_weights AS (
+            SELECT
+                user_id,
+                FIRST_VALUE(weight_kg) OVER (PARTITION BY user_id ORDER BY checked_in_at ASC)  AS first_weight,
+                FIRST_VALUE(weight_kg) OVER (PARTITION BY user_id ORDER BY checked_in_at DESC) AS current_weight,
+                ROW_NUMBER()           OVER (PARTITION BY user_id ORDER BY checked_in_at DESC) AS rn
+            FROM checkins
+        )
         SELECT
             u.id,
             u.display_name,
             u.username,
             u.starting_weight_kg,
-            (SELECT weight_kg FROM checkins WHERE user_id = u.id ORDER BY checked_in_at ASC LIMIT 1) as first_weight,
-            (SELECT weight_kg FROM checkins WHERE user_id = u.id ORDER BY checked_in_at DESC LIMIT 1) as current_weight
+            uw.first_weight,
+            uw.current_weight
         FROM users u
-        WHERE (SELECT COUNT(*) FROM checkins WHERE user_id = u.id) > 0
-          AND u.is_private = FALSE
+        JOIN user_weights uw ON uw.user_id = u.id AND uw.rn = 1
+        WHERE u.is_private = FALSE
         ORDER BY u.display_name
     """)