bionic (7) elektra-granularity.7.gz

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)