Handle mysql restart in SQLAlchemy

Question

My Pylons app uses local MySQL server via SQLAlchemy and python-MySQLdb. When the server is restarted, open pooled connections are apparently closed, but the application doe

Answer 1

You can use SQLAlchemy proxy for exception handling on each sql query:

from sqlalchemy.interfaces import ConnectionProxy
class MyProxy(ConnectionProxy):
    def cursor_execute(self, execute, cursor, statement, parameters, context, executemany):
        try:
            return execute(cursor, statement, parameters, context)
        except sqlalchemy.exc.OperationalError:
            # Handle this exception
            pass

To connect this proxy you must do that in config/enviroment.py

engine = engine_from_config(config, 'sqlalchemy.', proxy=MyProxy())

Or write middleware for exception handling on each http query:

class MyMiddleware(object):
    def __init__(self, app):
        self.app = app

    def __call__(self, environ, start_response):
        try:
            return self.app(environ, start_response)
        except sqlalchemy.exc.OperationalError:
            start_response(
                '500 Internal Server Error',
                [('content-type', 'text/html')])
            return ['error page\n']

To connect this middleware in stack order as you need or simply in config/middleware.py:

# CUSTOM MIDDLEWARE HERE (filtered by error handling middlewares)
app = MyMiddleware(app)