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.

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.