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

app/db.py

@@ -1,33 +1,41 @@
 import psycopg2
 import psycopg2.extras
+import psycopg2.pool
 from flask import g, current_app
 
+# Module-level connection pool (initialised once per process)
+_pool = None
+
 
 def init_db(app):
-    """Test the database connection on startup."""
+    """Initialise the connection pool on startup."""
+    global _pool
     try:
-        conn = psycopg2.connect(app.config["DATABASE_URL"])
-        conn.close()
-        print(" * Database connection OK")
+        _pool = psycopg2.pool.SimpleConnectionPool(
+            minconn=2,
+            maxconn=10,
+            dsn=app.config["DATABASE_URL"],
+        )
+        print(" * Database connection pool OK (2–10 connections)")
     except Exception as e:
-        print(f" * Database connection FAILED: {e}")
+        print(f" * Database connection pool FAILED: {e}")
 
 
 def get_db():
-    """Get a database connection for the current request."""
+    """Get a pooled database connection for the current request."""
     if "db" not in g:
-        g.db = psycopg2.connect(
-            current_app.config["DATABASE_URL"],
-            cursor_factory=psycopg2.extras.RealDictCursor,
-        )
+        g.db = _pool.getconn()
+        g.db.cursor_factory = psycopg2.extras.RealDictCursor
     return g.db
 
 
 def close_db(exception=None):
-    """Close database connection at end of request."""
+    """Return database connection to the pool at end of request."""
     db = g.pop("db", None)
     if db is not None:
-        db.close()
+        if exception:
+            db.rollback()
+        _pool.putconn(db)
 
 
 def query(sql, params=None):
@@ -62,3 +70,11 @@ def execute_returning(sql, params=None):
         row = cur.fetchone()
         db.commit()
         return row
+
+
+def execute_many(sql, params_list):
+    """Execute a batch INSERT/UPDATE/DELETE and commit."""
+    db = get_db()
+    with db.cursor() as cur:
+        cur.executemany(sql, params_list)
+        db.commit()