How -restrict_hosts Affects -fastload
You can use -fastload with -restrict_hosts. The performance improvement from -fastload will be less than if you did not use -restrict_hosts, but better than if you do not use -fastload. The usual cautions about -fastload apply; see Time vs. Correctness: Understanding -fastload Tradeoffs.
The -fastload and -restrict_hosts options interact as follows:
Without -restrict_hosts, mlcp figures out which hosts contains the destination forest for a document, and then connects directly to that host. When -restrict_hosts is true, a connection to the forest host might not possible. In this case, mlcp connects to an allowed e-node, and includes the detailed destination information along with the document. The destination details makes an insertion faster than it would otherwise be.