Tetra WebBBS Configuration
$SFU_redirects takes effect ONLY, if $SFU_subject is enabled!
If $SFU_redirects is set to '1' the script will validate incoming calls to message display pages to ensure the URLs used to access the message include the correct "sbj" parameter. If the "sbj" parameter is missing or is broken or not formatted according to the current settings of the board, then the scripts will answer with a "301 Moved Permanantly" redirect to inform the calling client about the changes made.
New in 6.10
The purpose of this feature is to ensure all calling clients are informed about changes in the hope the client will use this information for updating it's own database. The target of this features of course are spiders indexing the forum. It's supposed to help searchengines to update their databases as well as to avoid serving duplicate content to spiders if they access the forum by following older links on third-party websites.
Validating each incoming call for message display pages DOES put some additional load on a server.
Redirecting is fine if all goes well. Unfortunately there could be a situation where the client misinterprets the response or can't handle longer URLs. In such a (rare) case a redirect could result in an infinite loop until the client stops following redirects. In such a situation your server load can sky-rocket in fractions of a second. Severity of such a problem might depend on some configs but basically is due to the client and thus beyond the control of the forums.
As a result the simple advice is:
Do NOT enable this feature on any shared hosting account and do NOT enable unless you are familiar with reading logfiles and managing your virtual or dedicated server. Period. No exception.