~loggerhead-team/loggerhead/trunk-rich

Loggerhead

==========

Overview

--------

This document attempts to give some hints for people that are wanting to work

on Loggerhead.

Testing

-------

You can run the loggerhead test suite as a bzr plugin. To run just the

loggerhead tests::

  bzr selftest -s bp.loggerhead

Load Testing

------------

As a web service, Loggerhead will often be hit by multiple requests. We want

to make sure that loggerhead can scale with many requests, without performing

poorly or crashing under the load.

There is a command ``bzr load-test-loggerhead`` that can be run to stress

loggerhead. A script is given, describing what requests to make, against what

URLs, and for what level of parallel activity.

Load Testing Multiple Instances

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

One way that Launchpad provides both high availability and performance scaling

is by running multiple instances of loggerhead, serving the same content. A

proxy is then used to load balance the requests. This also allows us to shut

down one instance for upgrading, without interupting service (requests are

just routed to the other instance).

However, multiple processes poses an even greater risk that caches will

conflict. As such, it is useful to test that changes don't introduce coherency

issues at load. ``bzr load-test-loggerhead`` can be configured with a script

that will make requests against multiple loggerhead instances concurrently.

To run multiple instances, it is often sufficient to just spawn multiple

servers on different ports. For example::

  $ bzr serve --http --port=8080 &

  $ bzr serve --http --port=8081 &

There is a simple example script already in the source tree::

  $ bzr load-test-loggerhead load_test_scripts/multiple_instances.script

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