Chapter 16: Logging of slow database queries (16a)

Author: miguelgrinberg

app/main/views.py

@@ -1,6 +1,7 @@
 from flask import render_template, redirect, url_for, abort, flash, request,\
     current_app, make_response
 from flask_login import login_required, current_user
+from flask_sqlalchemy import get_debug_queries
 from . import main
 from .forms import EditProfileForm, EditProfileAdminForm, PostForm,\
     CommentForm
@@ -9,6 +10,17 @@
 from ..decorators import admin_required, permission_required
 
 
+@main.after_app_request
+def after_request(response):
+    for query in get_debug_queries():
+        if query.duration >= current_app.config['FLASKY_SLOW_DB_QUERY_TIME']:
+            current_app.logger.warning(
+                'Slow query: %s\nParameters: %s\nDuration: %fs\nContext: %s\n'
+                % (query.statement, query.parameters, query.duration,
+                   query.context))
+    return response
+
+
 @main.route('/shutdown')
 def server_shutdown():
     if not current_app.testing:

config.py

@@ -14,9 +14,11 @@ class Config:
     FLASKY_MAIL_SENDER = 'Flasky Admin <flasky@example.com>'
     FLASKY_ADMIN = os.environ.get('FLASKY_ADMIN')
     SQLALCHEMY_TRACK_MODIFICATIONS = False
+    SQLALCHEMY_RECORD_QUERIES = True
     FLASKY_POSTS_PER_PAGE = 20
     FLASKY_FOLLOWERS_PER_PAGE = 50
     FLASKY_COMMENTS_PER_PAGE = 30
+    FLASKY_SLOW_DB_QUERY_TIME = 0.5
 
     @staticmethod
     def init_app(app):