feat: optimize TTFB with connection pooling, caching, and performance monitoring

server.py

@@ -1,11 +1,12 @@
 import os
 import time
+import logging
 from threading import Thread
 import smtplib
 from email.mime.text import MIMEText
-from flask import Flask, render_template, request, jsonify
+from flask import Flask, render_template, request, jsonify, g
 from dotenv import load_dotenv
-from database import init_db, get_connection, add_email, remove_email
+from database import init_db, get_connection, return_connection, add_email, remove_email
 
 load_dotenv()
 
@@ -16,18 +17,14 @@ SMTP_PASSWORD = os.getenv('SMTP_PASSWORD')
 
 app = Flask(__name__)
 
-_db_initialized = False
+# Configure logging
+logging.basicConfig(level=logging.INFO)
+
+# Cache configuration
 _newsletter_cache = {}
 _cache_timestamp = {}
 CACHE_DURATION = 300
 
-def ensure_db_initialized():
-    """Lazy database initialization - only runs on first database access"""
-    global _db_initialized
-    if not _db_initialized:
-        init_db()
-        _db_initialized = True
-
 def get_newsletters_cached():
     """Get newsletters with caching to reduce database hits"""
     current_time = time.time()
@@ -36,26 +33,32 @@ def get_newsletters_cached():
         current_time - _cache_timestamp.get('newsletters', 0) < CACHE_DURATION):
         return _newsletter_cache['newsletters']
     
-    ensure_db_initialized()
-    conn = get_connection()
-    cursor = conn.cursor()
-    cursor.execute(
-        "SELECT id, subject, body, sent_at "
-        "FROM newsletters ORDER BY sent_at DESC"
-    )
-    rows = cursor.fetchall()
-    cursor.close()
-    conn.close()
-    
-    newsletters = [
-        {"id": r[0], "subject": r[1], "body": r[2], "sent_at": r[3]}
-        for r in rows
-    ]
-    
-    _newsletter_cache['newsletters'] = newsletters
-    _cache_timestamp['newsletters'] = current_time
-    
-    return newsletters
+    conn = None
+    try:
+        conn = get_connection()
+        cursor = conn.cursor()
+        cursor.execute(
+            "SELECT id, subject, body, sent_at "
+            "FROM newsletters ORDER BY sent_at DESC LIMIT 100"
+        )
+        rows = cursor.fetchall()
+        cursor.close()
+        
+        newsletters = [
+            {"id": r[0], "subject": r[1], "body": r[2], "sent_at": r[3]}
+            for r in rows
+        ]
+        
+        _newsletter_cache['newsletters'] = newsletters
+        _cache_timestamp['newsletters'] = current_time
+        
+        return newsletters
+    except Exception as e:
+        app.logger.error(f"Database error in get_newsletters_cached: {e}")
+        return []
+    finally:
+        if conn:
+            return_connection(conn)
 
 def get_newsletter_by_id_cached(newsletter_id):
     """Get single newsletter with caching"""
@@ -66,32 +69,38 @@ def get_newsletter_by_id_cached(newsletter_id):
         current_time - _cache_timestamp.get(cache_key, 0) < CACHE_DURATION):
         return _newsletter_cache[cache_key]
     
-    ensure_db_initialized()
-    conn = get_connection()
-    cursor = conn.cursor()
-    cursor.execute(
-        "SELECT id, subject, body, sent_at "
-        "FROM newsletters WHERE id = %s",
-        (newsletter_id,)
-    )
-    row = cursor.fetchone()
-    cursor.close()
-    conn.close()
-    
-    if not row:
-        return None
+    conn = None
+    try:
+        conn = get_connection()
+        cursor = conn.cursor()
+        cursor.execute(
+            "SELECT id, subject, body, sent_at "
+            "FROM newsletters WHERE id = %s",
+            (newsletter_id,)
+        )
+        row = cursor.fetchone()
+        cursor.close()
         
-    newsletter = {
-        "id": row[0],
-        "subject": row[1],
-        "body": row[2],
-        "sent_at": row[3]
-    }
-    
-    _newsletter_cache[cache_key] = newsletter
-    _cache_timestamp[cache_key] = current_time
-    
-    return newsletter
+        if not row:
+            return None
+            
+        newsletter = {
+            "id": row[0],
+            "subject": row[1],
+            "body": row[2],
+            "sent_at": row[3]
+        }
+        
+        _newsletter_cache[cache_key] = newsletter
+        _cache_timestamp[cache_key] = current_time
+        
+        return newsletter
+    except Exception as e:
+        app.logger.error(f"Database error in get_newsletter_by_id_cached: {e}")
+        return None
+    finally:
+        if conn:
+            return_connection(conn)
 
 def clear_newsletter_cache():
     """Clear newsletter cache when data is updated"""
@@ -103,35 +112,49 @@ def clear_newsletter_cache():
         _cache_timestamp.pop(key, None)
 
 @app.before_request
-def start_timer():
-    request._start_time = time.time()
+def before_request():
+    """Start timing the request and set up request context"""
+    g.start_time = time.time()
 
 @app.after_request
-def log_request(response):
-    elapsed = time.time() - getattr(request, '_start_time', time.time())
-    app.logger.info(f"{request.method} {request.path} completed in {elapsed:.3f}s")
+def after_request(response):
+    """Log request timing and performance metrics"""
+    total_time = time.time() - g.start_time
+    
+    # Log slow requests
+    if total_time > 1.0:
+        app.logger.warning(f"Slow request: {request.method} {request.path} took {total_time:.3f}s")
+    elif total_time > 0.5:
+        app.logger.info(f"Request: {request.method} {request.path} took {total_time:.3f}s")
+    
+    # Add performance headers for debugging
+    response.headers['X-Response-Time'] = f"{total_time:.3f}s"
+    
     return response
 
 def send_confirmation_email(to_address: str, unsubscribe_link: str):
     """
     Sends the HTML confirmation email to `to_address`.
-    This runs inside its own SMTP_SSL connection (timeout=10s).
+    This runs inside its own SMTP_SSL connection with reduced timeout.
     """
-    subject = "Thanks for subscribing!"
-    html_body = render_template(
-        "confirmation_email.html",
-        unsubscribe_link=unsubscribe_link
-    )
-
-    msg = MIMEText(html_body, "html", "utf-8")
-    msg["Subject"] = subject
-    msg["From"]    = SMTP_USER
-    msg["To"]      = to_address
-
     try:
-        with smtplib.SMTP_SSL(SMTP_SERVER, SMTP_PORT, timeout=10) as server:
+        subject = "Thanks for subscribing!"
+        html_body = render_template(
+            "confirmation_email.html",
+            unsubscribe_link=unsubscribe_link
+        )
+
+        msg = MIMEText(html_body, "html", "utf-8")
+        msg["Subject"] = subject
+        msg["From"] = SMTP_USER
+        msg["To"] = to_address
+
+        with smtplib.SMTP_SSL(SMTP_SERVER, SMTP_PORT, timeout=5) as server:
             server.login(SMTP_USER, SMTP_PASSWORD)
             server.sendmail(SMTP_USER, [to_address], msg.as_string())
+            
+        app.logger.info(f"Confirmation email sent successfully to {to_address}")
+        
     except Exception as e:
         app.logger.error(f"Failed to send email to {to_address}: {e}")
 
@@ -148,65 +171,113 @@ def index():
 
 @app.route("/subscribe", methods=["POST"])
 def subscribe():
-    """Subscribe endpoint - lazy loads database only when needed"""
+    """Subscribe endpoint with optimized database handling"""
     data = request.get_json() or {}
     email = data.get("email")
+    
     if not email:
         return jsonify(error="No email provided"), 400
 
-    ensure_db_initialized()
+    # Validate email format (basic check)
+    if "@" not in email or "." not in email.split("@")[-1]:
+        return jsonify(error="Invalid email format"), 400
     
-    if add_email(email):
-        unsubscribe_link = f"{request.url_root}unsubscribe?email={email}"
+    try:
+        if add_email(email):
+            unsubscribe_link = f"{request.url_root}unsubscribe?email={email}"
 
-        Thread(
-            target=send_confirmation_async,
-            args=(email, unsubscribe_link),
-            daemon=True
-        ).start()
+            # Start email sending in background thread
+            Thread(
+                target=send_confirmation_async,
+                args=(email, unsubscribe_link),
+                daemon=True
+            ).start()
 
-        return jsonify(message="Email has been added"), 201
-
-    return jsonify(error="Email already exists"), 400
+            return jsonify(message="Email has been added"), 201
+        else:
+            return jsonify(error="Email already exists"), 400
+            
+    except Exception as e:
+        app.logger.error(f"Error in subscribe endpoint: {e}")
+        return jsonify(error="Internal server error"), 500
 
 @app.route("/unsubscribe", methods=["GET"])
 def unsubscribe():
-    """Unsubscribe endpoint - lazy loads database only when needed"""
+    """Unsubscribe endpoint with optimized database handling"""
     email = request.args.get("email")
+    
     if not email:
         return "No email specified.", 400
 
-    ensure_db_initialized()
-    
-    if remove_email(email):
-        return f"The email {email} has been unsubscribed.", 200
-    return f"Email {email} was not found or has already been unsubscribed.", 400
+    try:
+        if remove_email(email):
+            return f"The email {email} has been unsubscribed.", 200
+        else:
+            return f"Email {email} was not found or has already been unsubscribed.", 400
+            
+    except Exception as e:
+        app.logger.error(f"Error in unsubscribe endpoint: {e}")
+        return "Internal server error", 500
 
 @app.route("/newsletters", methods=["GET"])
 def newsletters():
     """
     List all newsletters (newest first) with caching for better performance.
     """
-    newsletters = get_newsletters_cached()
-    return render_template("newsletters.html", newsletters=newsletters)
+    try:
+        newsletters = get_newsletters_cached()
+        return render_template("newsletters.html", newsletters=newsletters)
+    except Exception as e:
+        app.logger.error(f"Error in newsletters endpoint: {e}")
+        return "Internal server error", 500
 
 @app.route("/newsletter/<int:newsletter_id>", methods=["GET"])
 def newsletter_detail(newsletter_id):
     """
     Show a single newsletter by its ID with caching.
     """
-    newsletter = get_newsletter_by_id_cached(newsletter_id)
-    
-    if not newsletter:
-        return "Newsletter not found.", 404
+    try:
+        newsletter = get_newsletter_by_id_cached(newsletter_id)
+        
+        if not newsletter:
+            return "Newsletter not found.", 404
 
-    return render_template("newsletter_detail.html", newsletter=newsletter)
+        return render_template("newsletter_detail.html", newsletter=newsletter)
+    except Exception as e:
+        app.logger.error(f"Error in newsletter_detail endpoint: {e}")
+        return "Internal server error", 500
 
 @app.route("/admin/clear-cache", methods=["POST"])
 def clear_cache():
     """Admin endpoint to clear newsletter cache"""
-    clear_newsletter_cache()
-    return jsonify(message="Cache cleared successfully"), 200
+    try:
+        clear_newsletter_cache()
+        return jsonify(message="Cache cleared successfully"), 200
+    except Exception as e:
+        app.logger.error(f"Error clearing cache: {e}")
+        return jsonify(error="Failed to clear cache"), 500
+
+@app.route("/health", methods=["GET"])
+def health_check():
+    """Health check endpoint for monitoring"""
+    return jsonify(status="healthy", timestamp=time.time()), 200
+
+# Error handlers
+@app.errorhandler(404)
+def not_found(error):
+    return jsonify(error="Not found"), 404
+
+@app.errorhandler(500)
+def internal_error(error):
+    return jsonify(error="Internal server error"), 500
+
+# Initialize database at startup
+try:
+    init_db()
+    app.logger.info("Database initialized successfully")
+except Exception as e:
+    app.logger.error(f"Failed to initialize database: {e}")
+    raise
 
 if __name__ == "__main__":
     app.run(host="0.0.0.0", debug=True)