# 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.

- Kallithea is often I/O bound, and hence a fast disk (SSD/SAN) is usually more important than a fast CPU.
- Sluggish loading of the front page can easily be fixed by grouping repositories or by increasing cache size (see below). This includes using the lightweight dashboard option and `vcs_full_cache` setting in .ini file.

Follow these few steps to improve performance of Kallithea system.

1. Increase cache

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

2. 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.

3. 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 needs its own .ini file and unique `instance_id` set.
   > - 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.