If you have a set of files that regularly change over time: Old files
   are deleted, new ones are added, or existing files are modified, you
   can benefit from using the file ID
   indexing methodology.
   Examples of this type of database might include an index of WWW
   resources, or a USENET news spool area.
   Briefly speaking, the file key methodology uses the directory paths
   of the individual records as a unique identifier for each record.
   To perform indexing of a directory with file keys, again, you specify
   the top-level directory after the update command.
   The command will recursively traverse the directories and compare
   each one with whatever have been indexed before in that same directory.
   If a file is new (not in the previous version of the directory) it
   is inserted into the registers; if a file was already indexed and
   it has been modified since the last update, the index is also
   modified; if a file has been removed since the last
   visit, it is deleted from the index.
  
   The resulting system is easy to administrate. To delete a record you
   simply have to delete the corresponding file (say, with the
   rm command). And to add records you create new
   files (or directories with files). For your changes to take effect
   in the register you must run zebraidx update with
   the same directory root again. This mode of operation requires more
   disk space than simpler indexing methods, but it makes it easier for
   you to keep the index in sync with a frequently changing set of data.
   If you combine this system with the safe update
   facility (see below), you never have to take your server off-line for
   maintenance or register updating purposes.
  
   To enable indexing with pathname IDs, you must specify
   file as the value of recordId
   in the configuration file. In addition, you should set
   storeKeys to 1, since the Zebra
   indexer must save additional information about the contents of each record
   in order to modify the indexes correctly at a later time.
  
   For example, to update records of group esdd
   located below
   /data1/records/ you should type:
   
    $ zebraidx -g esdd update /data1/records
   
The corresponding configuration file includes:
    esdd.recordId: file
    esdd.recordType: grs.sgml
    esdd.storeKeys: 1
   
You cannot start out with a group of records with simple indexing (no record IDs as in the previous section) and then later enable file record Ids. Zebra must know from the first time that you index the group that the files should be indexed with file record IDs.
   You cannot explicitly delete records when using this method (using the
   delete command to zebraidx. Instead
   you have to delete the files from the file system (or move them to a
   different location)
   and then run zebraidx with the
   update command.