docs: tweak formatting of the performance page - replace the odd numbered list with sections

docs/usage/performance.rst

@@ -1,99 +1,112 b''
 .. _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.
+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.
+
+Fast storage
+------------
 
-1.  Kallithea is often I/O bound, and hence a fast disk (SSD/SAN) is
-    usually more important than a fast CPU.
+Kallithea is often I/O bound, and hence a fast disk (SSD/SAN) and plenty of RAM
+is usually more important than a fast CPU.
 
-2. Increase cache
+
+Caching
+-------
 
-    Tweak beaker cache settings in the ini file. The actual effect of that
-    is questionable.
+Tweak beaker cache settings in the ini file. The actual effect of that is
+questionable.
 
-3. Switch from SQLite to PostgreSQL or MySQL
+
+Database
+--------
 
     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.
+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
+Horizontal scaling
+------------------
 
-    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.
+Scaling horizontally means running several Kallithea instances and let them
+share the load. That 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.
 
     It is generally possible to run WSGI applications multithreaded, so that
-    several HTTP requests are served from the same Python process at once. That
-    can in principle give better utilization of internal caches and less
-    process overhead.
+several HTTP requests are served from the same Python process at once. That can
+in principle give better utilization of internal caches and less process
+overhead.
 
-    One danger of running multithreaded is that program execution becomes much
-    more complex; programs must be written to consider all combinations of
-    events and problems might depend on timing and be impossible to reproduce.
+One danger of running multithreaded is that program execution becomes much more
+complex; programs must be written to consider all combinations of events and
+problems might depend on timing and be impossible to reproduce.
 
     Kallithea can't promise to be thread-safe, just like the embedded Mercurial
     backend doesn't make any strong promises when used as Kallithea uses it.
     Instead, we recommend scaling by using multiple server processes.
 
     Web servers with multiple worker processes (such as ``mod_wsgi`` with the
     ``WSGIDaemonProcess`` ``processes`` parameter) will work out of the box.
 
     In order to scale horizontally on multiple machines, 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 using several Celery instances,
       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
+
+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.
 
 
 .. _SQLAlchemyGrate: https://github.com/shazow/sqlalchemygrate