Specifies the java class used for the frontier (a list of URLs not yet visited).

Key: crawler.classes.Frontier
Type: String
Can be set in: collection.cfg


The web crawler’s frontier is the queue of URLs that are waiting to be processed. The following are the main frontier types available:

  • (default) Supports sending multiple parallel requests to servers as specified in site profiles configuration.

  • Uses separate queues for each host. The host frontier guarantees that the crawler will never have more than one active request with any host at any time.

  • This is a first-in first-out (FIFO) management scheme. Using this frontier allows the crawler to create multiple simultaneous connections to a target host. Using the FIFO frontier with 5 crawler threads (num_crawlers=5) means that a host could potentially receive 5 simultaneous requests from Funnelabck at any given time.

FIFO frontier can generate heavy load on a target web server.

Default Value

This specifies that a MultipleRequestsFrontier should be used, which in turn makes use of disk-based FIFOFrontiers of size 1000 each. Here size refers to the number of URLs per frontier i.e. in the example above each disk-based FIFOFrontier will store up to 1000 URLs each. When a frontier fills up a new one will be created so that all the URLs in the entire frontier are stored in a chain of backing frontiers.