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Logjam is a Ruby on Rails application for finding performance hot spots and errors in web applications. Its primary target are Ruby on Rails applications, although it's possible to use it with other technologies.

It differs from other Rails monitoring solutions in that is is meant to be hosted in your own data center (or private cloud), for two reasons:

  • it requires low latency between the monitored application and itself
  • it stores extensive information for web requests, which might contain sensitive data

Logjam can produce various graphs and tables showing how much time and memory are consumed by different parts of your application. The interface is flexible enough to be able to provide answers to a great many questions you may have about your application, such as

  • which actions in my application are most in need of optimization?
  • in the worst case, how slow is my application?
  • which actions are causing the most exceptions?
  • what actions are causing the ruby heap to grow?
  • which actions are making the most DB queries?
  • which actions spend most of their time waiting for external services?
  • how is my application behaving currently?

It also provides a live stream of performance and error data which is especially useful for supervising applications during deployments.

In addition, if you have several applications to monitor, and they call each other, Logjam can show you how often and when these calls occur.

Note that some of Logjam's features (e.g. those involving GC and memory data) depend on using a specially built version of Ruby (see

Quick start for the impatient developer

A quick way of getting to understand what Logjam can do is to install and run a local development version, which monitors itself.

In the following, I assume you're a Rails developer.

Install required software packages

If you're on a Mac and are using MacPorts:

sudo port install mongodb memcached

I'm sure with Home Brew it's equally simple, but I haven't tried it.

In either case, you might need to create the mongodb data directory:

sudo mkdir -p /data/db

If you're using rvm, I recommend to install a patched ruby like so:

rvm install 2.3.3-railsexpress --patch railsexpress
rvm use 2.3.3-railsexpress@logjam --create
gem install bundler

Note: make sure to have a recent rvm version installed, otherwise it will not have up to date ruby patches. If in doubt, run

rvm get latest

Please follow the instructions on to install logjam tools.

Clone the git repository and bundle the application

git clone
cd logjam_app
git submodule init
git submodule update
echo 2.3.3-railsexpress > .ruby-version
echo logjam > .ruby-gemset
cd .
mkdir -p log

Start the services and initialize the database


rake logjam:daemons:install

to create necessary service definitions under ./service.

Open a separate terminal session and run

foreman start

foreman will start all background processes which are necessary to enable self monitoring. If this gives you errors, e.g. because you have mongodb or memcached already running on your machine, comment out the corresponging lines in ./Procfile.

Then go back to the original session and run

rake logjam:db:update_known_databases

to initialize mongodb contents.

Start the application and play

Run "rails s", then open the browser at http://localhost:3000/. You will be greeted with a "Dataset Empty" message. Reload the page to get some performance data. Then click around and explore the UI while your dataset continues to grow.


If you experience any problems following the steps above, please open a ticket.

Monitoring other applications

Unsurprisingly, this requires you to configure Logjam to listen for request information and the application to send request data.

Transport options

Logjam supports two different transport methods for sending request information from the application to Logjam:

  • AMQP
  • ZeroMQ

AMQP was the first transport to be implemented when all the importer code was still in ruby. It requires a running message broker and a corresponding logjam-device to publish messages for the importer process, but does not require ZMQ libraries to be installed on machines running message publishers. Nowadays, I consider it mostly deprecated, but if you prefer it, RabbitMQ is a good broker choice.

With ZeroMQ, the application can either talk directly to the logjam request import daemon or a logjam-device can be used as an intermediate. The logjam-tools README has more details abut port usage of importer, devices and other daemons.

Configuring Logjam

Application monitoring is configured through stream declarations in the file ./config/initializers/logjam_streams.rb. In the simplest case, such a declaration looks like this:

stream "app-env"

Here app is the name which will be used by logjam internally and "env" the name of the environment (typically "production").

Instrumenting the application

  • add the logjam_agent gem to the Gemfile of your application
  • add an initializer for logjam_agent and specify transport method and endpoint
  • add either the bunny gem or the ffi-rzmq gem to the Gemfile (depending on which transport you chose)
  • add an initializer for time_bandits gem and specify which metrics to track

Have a look at the corresponding files in logjam itself to get an idea on how to proceed.

Deploying Logjam into production

Contact the author ...


Stefan Kaes ( and David Anderson (


Older versions of this code were MIT licensed. The current license version is GPLv3.

Copyright (c) 2009-2017 Stefan Kaes

Copyright (c) 2009 David Anderson

Copyright (c) 2009 XING AG

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see


A rails application wrapper for the logjam plugin.







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