Index only documents that are absent from the index. Any document that has been previously indexed will not be checked for changes. This allows to restart indexing from the abandoned point and to index only newly added documents to the files pointed by the UrlListFile directive.
Enabling this option is not suitable for background indexing or reindexing of a previously built database from command line. It is intended for sites maintaining full lists of urls collected from users or generated dynamically.
This option can be forced from the command line with --newonly .