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)