Overview

The slowlog library helps you find out why some requests to your web application take a long time. It periodically dumps stack traces of long running requests to a log file. It works as a Pyramid tween or as a WSGI component. It is inspired by Products.LongRequestLogger, which provides similar functionality for Zope 2.

This library can also log frame statistics to Graphite using the perfmetrics library, making it possible to create real-time graphs that reveal expensive code paths.

This library uses sys._current_frames() to gather stack traces, so it supports CPython versions 2.6+ and 3.2+, but other Python implementations might not work.

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Installation

Install using setuptools, e.g. (within a virtualenv)::

$ bin/easy_install slowlog

Pyramid Configuration

Once the slowlog library is installed, use the config.include mechanism to add slowlog to your project. In your Pyramid project's __init__.py::

config = Configurator(...)
config.include('slowlog')

Alternately, you can add the following line to your application's .ini file::

pyramid.includes = slowlog

Next, Pyramid needs some settings before the slowlog library has any effect. Two tweens are available, slowlog and framestats.

The slowlog tween

The ``slowlog`` tween periodically logs stack traces of long running
requests.  To activate it, set ``slowlog = true`` in your Pyramid settings.
The ``slowlog`` tween supports the following settings.

slowlog
    Set to ``true`` to activate the ``slowlog`` tween.  Default: false.

slowlog_timeout
    Only log stack traces of requests that last at least
    this number of seconds (floating point).  Default: 2.0.

slowlog_interval
    Once a request lasts longer than ``slowlog_timeout``, the
    ``slowlog`` tween continues to log stack traces periodically with
    the given interval in seconds (floating point). Default: 1.0.

slowlog_file
    Log all stack traces to the given file.  The file will be rotated
    automatically when it grows to 10 megabytes.  If this setting is empty or
    missing, stack traces will be logged using Python's standard
    ``logging`` module with the logger name ``slowlog``.  Default: none.

slowlog_frames
    Limit the number of frames in stack traces.  If set to 0, no stack
    traces will be logged.  Default: 100.

slowlog_hide_post_vars
    A whitespace-delimited list of POST variables that should be
    redacted (hidden) in logs.  Useful for avoiding accidental storage
    of cleartext passwords.  Default:  ``password``.

The framestats tween

The framestats tween periodically increments Statsd counters for all frames on the stack of long-running requests. To activate it, set framestats = true in your Pyramid settings. The framestats tween supports the following settings.

framestats Set to true to activate the framestats tween. Default: false.

statsd_uri Required. A common URI is statsd://localhost:8125. See the perfmetrics library for supported parameters.

framestats_timeout Only update Statsd for requests that last at least this number of seconds (floating point). Default: 2.0.

framestats_interval Once a request lasts longer than framestats_timeout, the framestats tween continues to update Statsd periodically with the given interval in seconds (floating point). Default: 1.0.

framestats_frames Limit the number of frames to follow in stack traces. If set to 1, Statsd will receive information about only the current frame. Default: 100.