facets_protection
For some time now, excessive bot traffic has been causing overload on faceted views. The new version 3 of Facets already addresses this issue and offers the option of integrating facets as exposed filters in Views. This module aims to provide additional protection for existing facets until they are migrated to version 3 and exposed filters, which is often a matter of time and/or budget constraints.
This module appends tokens to facet links that are valid for a limited time. This validity period can be set in the backend.
If the token is missing or invalid, a blocking page will be shown. After 2.5 seconds the new links appears and can be clicked. This blocking page can be adapted via theme file.
The protection only works against bots that traverse previously cached URLs. This module is ineffective against bots that crawl the site in real time.
The module Facet Bot Blocker offers a different approach, limiting the maximum number of facets that can be selected.
See also this blog article by @capellic