NAME

       elektra-granularity - relation of keys to files

       Keys  of  a backend can only be retrieved as a full key set. Currently it is not possible to fetch a part
       of the keys of a backend. So the user needs to cut out the interesting keys with ksCut()  afterwards.  If
       the keys should be committed again, the whole key set must be preserved. Otherwise, the clipped keys will
       be removed permanently.

       This  restriction simplifies storage plugins while it does not limit the user. Other plugins would not be
       able to fulfil their purpose without the full KeySet. For example, a plugin that checks the  availability
       and structure of all keys cannot work with a partial key set.

       It  is  problematic  to  have  too  many  keys  in  one  backend.  The applications would need memory for
       unnecessary configuration data. Instead we recommend introducing several mount points  to  split  up  the
       keys  into  different backends. Splitting up key sets makes sense if any application requests only a part
       of the configuration. No benefits arise if every application requests all keys anyway.

       Let us assume that many keys reside in user/sw and an application only needs the keys in user/sw/app.  To
       save  memory  and  get  better  startup  times  for  the  application,  a  new  backend can be mounted at
       user/sw/app. On the other hand, every mounted backend causes a small run time  overhead  in  the  overall
       configuration system.

       The  solution in Elektra is flexible, because the user decides the granularity. It is possible to mount a
       backend on every single key, so that every key can be requested for itself. If no backends  are  mounted,
       all keys reside in the default backend.

       To  sum up, Elektra´s core searches for the nearest mount point and gets the configuration from there. It
       is possible that the user gets more configuration than  requested.  The  user  can  decide  by  means  of
       mounting how much configuration on specific requests are returned.

                                                    July 2017                             ELEKTRA-GRANULARITY(7)