icm/HTTP/server_cache_<xx>/ufo_list
This parameter is set to the logical value ‘TRUE’ in order to activate the UFO (‘un-found objects’) list of the ICM/HTTP server cache. This list is a negative list of all HTTP URLs that are invalid or unknown to the system.
The purpose of this list is to ensure that all HTTP requests that have been rejected by the system in the past continue to be rejected in future rejected by the cache. In this way, such requests do not add to the load on the application server the second time round (sporadic errors, denial-of-service attacks).
It is therefore important that every entry in the UFO list has an expiry time attached, similarly to the entries in the cache itself (see also
icm/HTTP/server_cache_<xx>/ufo_expiration).
When configuring the UFO list, pay particular attention to the memory requirements for the access index stored in main memory.
Rule of Thumb for Calculating Memory Requirements
Requirement (bytes) = 2 * max_ufo_entries * max_name_len
In Unicode systems, the requirement is approximately twice as high.
Value Range |
Unit |
Default Setting |
TRUE, FALSE |
Boole |
FALSE |