Development Tips
================

If you are doing development on the Ray codebase, the following tips may be
helpful.

1. **Speeding up compilation:** Be sure to install Ray with

   .. code-block:: shell

     cd ray/python
     pip install -e . --verbose

   The ``-e`` means "editable", so changes you make to files in the Ray
   directory will take effect without reinstalling the package. In contrast, if
   you do ``python setup.py install``, files will be copied from the Ray
   directory to a directory of Python packages (often something like
   ``/home/ubuntu/anaconda3/lib/python3.6/site-packages/ray``). This means that
   changes you make to files in the Ray directory will not have any effect.

   If you run into **Permission Denied** errors when running ``pip install``,
   you can try adding ``--user``. You may also need to run something like ``sudo
   chown -R $USER /home/ubuntu/anaconda3`` (substituting in the appropriate
   path).

   If you make changes to the C++ files, you will need to recompile them.
   However, you do not need to rerun ``pip install -e .``. Instead, you can
   recompile much more quickly by doing

   .. code-block:: shell

     cd ray/python/ray/core
     make -j8

2. **Starting processes in a debugger:** When processes are crashing, it is
   often useful to start them in a debugger (``gdb`` on Linux or ``lldb`` on
   MacOS). See the latest discussion about how to do this `here`_.

3. **Running tests locally:** Suppose that one of the tests (e.g.,
   ``runtest.py``) is failing. You can run that test locally by running
   ``python test/runtest.py``. However, doing so will run all of the tests which
   can take a while. To run a specific test that is failing, you can do

   .. code-block:: shell

     cd ray
     python test/runtest.py APITest.testKeywordArgs

   When running tests, usually only the first test failure matters. A single
   test failure often triggers the failure of subsequent tests in the same
   script.

4. **Running linter locally:** To run the Python linter on a specific file, run
   something like ``flake8 ray/python/ray/worker.py``. You may need to first run
   ``pip install flake8``.

5. **Inspecting Redis shards by hand:** To inspect the primary Redis shard by
   hand, you can query it with commands like the following.

   .. code-block:: python

     r_primary = ray.worker.global_worker.redis_client
     r_primary.keys("*")

   To inspect other Redis shards, you will need to create a new Redis client.
   For example (assuming the relevant IP address is ``127.0.0.1`` and the
   relevant port is ``1234``), you can do this as follows.

   .. code-block:: python

     import redis
     r = redis.StrictRedis(host='127.0.0.1', port=1234)

   You can find a list of the relevant IP addresses and ports by running

   .. code-block:: python

     r_primary.lrange('RedisShards', 0, -1)

.. _`here`: https://github.com/ray-project/ray/issues/108