HoldBadHrefs defines period of time to keep unavailable documents (with bad status, e.g. 404 Not found or 503 Service unavailable) before deleting them from the database.
When indexer finds that a remote host is down, the documents from this site are not deleted from the database immediately and search.cgi uses the previous content of these documents. However, if the site doesn't respond for a long period of time (e.g. a month), it should be fine to remove its documents from the database.
The default value is 0, which means never delete unavailable documents from the database automatically (for better crawling performance).
Note: You can periodically delete bad documents from the database manually, using indexer with the
-scommand line parameter (status limit), for example: indexer -Cw -s404.
See Period for the time format description.