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domruf

vcs: fix processing of git commands that return output on stderr

The subprocessio module used for interfacing with Git is using threading. It
might not be fully deterministic.

The subprocessio module also had the "feature" that it stopped reading and
reported failure once it found output on stderr - even if the command completed
(or would complete) with success.

Sometimes (like https://drone.io/bitbucket.org/domruf/kallithea/24 ) tests on
linux could fail on totally normal informational output like:

Couldn't run git command (['git', '-c', 'core.quotepath=false', 'checkout', 'foobranch']).
Original error was: Subprocess exited due to an error:
Switched to branch 'foobranch'

On Windows it would fail even more often.

To fix that, ignore stderr while processing output. There is a risk that it in
some cases can make the process block on stderr and thus never finish ... but
there is no reports of that yet.

.. _performance:

================================
Optimizing Kallithea performance
================================

When serving a large amount of big repositories, Kallithea can start
performing slower than expected. Because of the demanding nature of handling large
amounts of data from version control systems, here are some tips on how to get
the best performance.

Follow these few steps to improve performance of Kallithea system.

1.  Kallithea is often I/O bound, and hence a fast disk (SSD/SAN) is
    usually more important than a fast CPU.

2. Increase cache

    Tweak beaker cache settings in the ini file. The actual effect of that
    is questionable.

3. Switch from SQLite to PostgreSQL or MySQL

    SQLite is a good option when having a small load on the system. But due to
    locking issues with SQLite, it is not recommended to use it for larger
    deployments. Switching to MySQL or PostgreSQL will result in an immediate
    performance increase. A tool like SQLAlchemyGrate_ can be used for
    migrating to another database platform.

4. Scale Kallithea horizontally

    Scaling horizontally can give huge performance benefits when dealing with
    large amounts of traffic (many users, CI servers, etc.). Kallithea can be
    scaled horizontally on one (recommended) or multiple machines. In order
    to scale horizontally you need to do the following:

    - Each instance's ``data`` storage needs to be configured to be stored on a
      shared disk storage, preferably together with repositories. This ``data``
      dir contains template caches, sessions, whoosh index and is used for
      task locking (so it is safe across multiple instances). Set the
      ``cache_dir``, ``index_dir``, ``beaker.cache.data_dir``, ``beaker.cache.lock_dir``
      variables in each .ini file to a shared location across Kallithea instances
    - If celery is used each instance should run a separate Celery instance, but
      the message broker should be common to all of them (e.g.,  one
      shared RabbitMQ server)
    - Load balance using round robin or IP hash, recommended is writing LB rules
      that will separate regular user traffic from automated processes like CI
      servers or build bots.


.. _SQLAlchemyGrate: https://github.com/shazow/sqlalchemygrate