Metadata-Version: 1.0
Name: dogslow
Version: 0.6
Summary: A Django middleware that logs tracebacks of slow requests.
Home-page: https://bitbucket.org/evzijst/dogslow
Author: Erik van Zijst
Author-email: erik.van.zijst@gmail.com
License: GNU LGPL
Download-URL: https://bitbucket.org/evzijst/dogslow/downloads/dogslow-0.6.tar.gz
Description: =======================================
        Dogslow -- Django Slow Request Watchdog
        =======================================
        
        
        Overview
        --------
        
        Dogslow is Django watchdog middleware class that logs tracebacks of slow
        requests.
        
        It started as an `internal project inside Bitbucket`_ to help trace
        operational problems.
        
        .. _internal project inside Bitbucket: http://blog.bitbucket.org/2011/05/17/tracking-slow-requests-with-dogslow/
        
        
        Installation
        ------------
        
        Install dogslow::
        
            $ pip install dogslow
        
        Then add if to your list of middleware classes in your Django settings.py file::
        
            MIDDLEWARE_CLASSES = (
                'dogslow.WatchdogMiddleware',
                ...
            )
        
        For best results, make it one of the first middlewares that is run.
        
        
        Configuration
        -------------
        
        You can use the following configuration properties in your ``settings.py``
        file to tune the watchdog::
        
            # Watchdog is enabled by default, to temporarily disable, set to False:
            DOGSLOW = True
        
            # Location where Watchdog stores its log files:
            DOGSLOW_OUTPUT = '/tmp'
        
            # Log requests taking longer than 25 seconds:
            DOGSLOW_TIMER = 25
        
            # When both specified, emails backtraces:
            DOGSLOW_EMAIL_TO = 'errors@atlassian.com'
            DOGSLOW_EMAIL_FROM = 'no-reply@atlassian.com'
        
        
        Usage
        -----
        
        Every incoming HTTP request gets a 25 second timeout in the watchdog. If a
        request does not return within that time, the watchdog activates and takes a
        peek at the request thread's stack and writes the backtrace (including all
        local stack variables -- Django style) to a log file.
        
        Each slow request is logged in a separate file that looks like this::
        
            Undead request intercepted at: 16-05-2011 02:10:12 UTC
        
            GET http://localhost:8000/?delay=2
            Thread ID:  140539485042432
            Process ID: 18010
            Parent PID: 17762
            Started:    16-05-2011 02:10:10 UTC
        
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 107, in inner_run
                run(self.addr, int(self.port), handler, ipv6=self.use_ipv6)
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 696, in run
                httpd.serve_forever()
              File "/usr/lib/python2.7/SocketServer.py", line 227, in serve_forever
                self._handle_request_noblock()
              File "/usr/lib/python2.7/SocketServer.py", line 284, in _handle_request_noblock
                self.process_request(request, client_address)
              File "/usr/lib/python2.7/SocketServer.py", line 310, in process_request
                self.finish_request(request, client_address)
              File "/usr/lib/python2.7/SocketServer.py", line 323, in finish_request
                self.RequestHandlerClass(request, client_address, self)
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 570, in __init__
                BaseHTTPRequestHandler.__init__(self, *args, **kwargs)
              File "/usr/lib/python2.7/SocketServer.py", line 639, in __init__
                self.handle()
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 615, in handle
                handler.run(self.server.get_app())
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/servers/basehttp.py", line 283, in run
                self.result = application(self.environ, self.start_response)
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/contrib/staticfiles/handlers.py", line 68, in __call__
                return self.application(environ, start_response)
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/handlers/wsgi.py", line 273, in __call__
                response = self.get_response(request)
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/handlers/base.py", line 111, in get_response
                response = callback(request, *callback_args, **callback_kwargs)
              File "/home/erik/work/middleware/middleware/sleep/views.py", line 6, in sleep
                time.sleep(float(request.GET.get('delay', 1)))
        
            Full backtrace with local variables:
        
              File "/home/erik/work/virtualenv/bit/lib/python2.7/site-packages/django/core/management/commands/runserver.py", line 107, in inner_run
                run(self.addr, int(self.port), handler, ipv6=self.use_ipv6)
        
              ...loads more...
        
        The example above shows that the request thread was blocked in
        ``time.sleep()`` at the time ``dogslow`` took its snapshot.
        
        Requests that return before ``dogslow``'s timeout expires do not get logged.
        
        Note that ``dogslow`` only takes a peek at the thread's stack. It does not
        interrupt the request, or influence it in any other way. Using ``dogslow`` is
        therefore safe to use in production.
        
        
        Caveats
        -------
        
        Dogslow uses multithreading. It has a single background thread the handles the
        watchdog timeouts and takes the tracebacks, so that the original request
        threads are not interrupted. This has some consequences.
        
        
        Multithreading and the GIL
        ~~~~~~~~~~~~~~~~~~~~~~~~~~
        
        In cPython, the GIL (Global Interpreter Lock) prevents multiple threads from
        executing Python code simultaneously. Only when a thread explicitly releases
        its lock on the GIL, can a second thread run.
        
        Releasing the GIL is done automatically whenever a Python program makes
        blocking calls outside of the interpreter, for example when doing IO.
        
        For ``dogslow`` this means that it can only reliably intercept requests that
        are slow because they are doing IO, calling sleep or busy waiting to acquire
        locks themselves.
        
        In most cases this is fine. An important cause of slow Django requests is an
        expensive database query. Since this is IO, ``dogslow`` can intercept those fine.
        A scenario where cPython's GIL is problematic is when the request's thread hits
        an infinite loop in Python code (or legitimate Python that is extremely
        expensive and takes a long time to execute), never releasing the GIL. Even
        though ``dogslow``'s watchdog timer does become runnable, it cannot log the
        stack.
        
        
        Co-routines and Greenlets
        ~~~~~~~~~~~~~~~~~~~~~~~~~
        
        ``Dogslow`` is intended for use in a synchronous worker configuration. A
        webserver that uses dedicated threads (or single-threaded, dedicated worker
        processes) to serve requests. Django's built-in wsgi server does this, as
        does ``Gunicorn`` in its default sync-worker mode.
        
        When running with a "co-routines framework" where multiple requests are served
        concurrently by one thread, backtraces might become nonsensical.
        
Keywords: django debug watchdog middleware
Platform: UNKNOWN
Classifier: Development Status :: 4 - Beta
Classifier: Framework :: Django
Classifier: Intended Audience :: Developers
Classifier: License :: OSI Approved :: GNU Library or Lesser General Public License (LGPL)
Classifier: Natural Language :: English
Classifier: Operating System :: OS Independent
Classifier: Programming Language :: Python :: 2.5
Classifier: Programming Language :: Python :: 2.6
Classifier: Programming Language :: Python :: 2.7
Classifier: Topic :: Utilities
