NAME

       md_doc_help_elektra-backendselektra-backends(7) -- the backend concept
        - Elektra has introduced *backends** to support the storage of key databases in different
       formats. Elektra abstracts configuration so that applications can receive and store
       settings without carrying information about how and where these are actually stored. It is
       the purpose of the backends to implement these details.

       Since Elektra 0.8 a backend is composed of many plugins.

       Its clear that too many features in one backend is problematic. It introduces unwanted
       external dependences and leads to less portable backends. Many different aspects clutter
       the code making the backends unmaintainable. Features of other backends cannot be taken
       with ease because they are interwoven with other code.

       To support the reuse of a functionality, they must be useful in different situations.
       Separation of concerns is required for that. Each backend needs to have a specific purpose
       rather than implementing the full semantics of Elektra.

       It was impossible to implement powerful and feature-rich backends so far because of the
       lack of modularity. Desirable features like notification and type checking have always
       been in the developers' heads, but there was no place where it would fit in without making
       the system unmaintainable, complex and full of unwanted external dependences.

       To solve this dilemma, Elektra uses multiple plugins together build up a backend. The key
       set processed by one plugin will be passed to the next. This approach allows us to
       implement separate features in separate plugins. Plugins concerned with reading and
       writing to permanent storage are called storage plugins. We cleaned existing backends from
       other tasks so that their only job now is related to the storage. Using this approach, the
       plugins provide the desired separation of concerns inside a backend.

       Each plugin implements a single concrete requirement and it does that well. This
       architecture allows plugins to have external dependence. Not every plugin has the burden
       to be portable anymore. That is no problem because the plugins are separate subprojects
       and maintainers can decide if they should be built for a specific platform or not.
       Afterwards users can choose which plugins they want to install and use. And finally, the
       administrator can choose which of the plugins should be loaded for each backend. If a
       specific feature is not needed, it is not included and does not cause additional overhead.
       Given the chosen approach, the core of Elektra can stay minimal. Most functionality can be
       moved to plugins.

       Now let us look at the development time with multiple plugins. The programmer will find
       many reusable plugins. Some of them already fulfil given requirements. While checking the
       code quality of the plugins, the programmer actually learns how the plugin works. Given
       that point of view, the programmer will decide to use Elektra because he or she can choose
       from a pool of existing plugins.

   SEE ALSO
       • More information about elektra-plugins(7)

       • The tool for mounting a backend is kdb-mount(1)

       • The plugins are ordered as described in elektra-plugins-ordering(7)