Contributing to the performance drive
=====================================

.. contents:: :local:

What needs doing?
-----------------

There is plenty of code to write. Testers are always welcome for experimental
changes. In general, pick a BLUE node from performance.png which has nothing
pointing at it that is also BLUE, and start working on that.

Adhoc performance work can also be done. One useful tool is the 'evil' debug
flag. For instance running ``bzr -Devil commit -m "test"`` will log a backtrace
to the bzr log file for every method call which triggers a slow or non-scalable
part of the bzr library. So checking that a given command with ``-Devil`` has
no backtraces logged to the log file is a good way to find problem function
calls that might be nested deep in the code base.

Status
------

The performance drive is well under way. At the moment we are finalising the
analysis documents from the sprint at London. If you were not at that sprint,
please read the analysis documents - consider them living documents much like
code, to be patched and corrected.

If you were at the London performance sprint, please help finish documenting
the core command analysis work. The core commands that have not been analysed
are listed in performance.dot as the BLUE nodes. For quick reference:

* status
* log
* diff
* uncommit
* missing
* update
* cbranch

Once a given command has had its analysis created, the bottleneck of 'folk who
attended London' is removed. The next task is in general the creation of a
targeted API stack for that command. This API stack is done by starting with
the cmd object in ``builtins.py`` and cleaning up the code so that the API used
there is one which allows an implementation matching the analysis document.
This then gets repeated, iteratively, on each of the called API's, until all
the current slow code is cleanly abstracted behind the ``Tree``, ``Branch`` and
``Repository`` API's.

Resources
---------

The usual resources for contributing to bzr - the mailing list, wiki, bug
tracker and IRC channels are documented in the HACKING_ document. Additionally
there are members of the project focusing on performance at the moment who are
willing to mentor contributors on performance issues. Just send a mail to the
list asking for mentoring on the step of the performance plan you want to help
with.

.. _HACKING: HACKING.htm
