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.

5. Serve static files directly from the web server

With the default static_files ini setting, the Kallithea WSGI application will take care of serving the static files found in kallithea/public from the root of the application URL. While doing that, it will currently also apply buffering and compression of all the responses it is serving.

The actual serving of the static files is unlikely to be a problem in a Kallithea setup. The buffering of responses is more likely to be a problem; large responses (clones or pulls) will have to be fully processed and spooled to disk or memory before the client will see any response.

To serve static files from the web server, use something like this Apache config snippet:

Alias /images/ /srv/kallithea/kallithea/kallithea/public/images/
Alias /css/ /srv/kallithea/kallithea/kallithea/public/css/
Alias /js/ /srv/kallithea/kallithea/kallithea/public/js/
Alias /codemirror/ /srv/kallithea/kallithea/kallithea/public/codemirror/
Alias /fontello/ /srv/kallithea/kallithea/kallithea/public/fontello/

Then disable serving of static files in the .ini app:main section:

static_files = false

If using Kallithea installed as a package, you should be able to find the files under site-packages/kallithea, either in your Python installation or in your virtualenv. When upgrading, make sure to update the web server configuration too if necessary.