Zebra - User's Guide and Reference
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# Indexing with File Record IDs

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

> Note: 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.

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