If mod_proxy_fcgi is handling a request it encounters an error sending data to the client (most commonly because the client has disconnected) then it will often stop processing data in the middle of an FCGI record and return from dispatch() without having read the entire record from the FCGI server. When dispatch() is next entered it tries to read a new record, but gets bogus data from the middle of the previous record and logs an error along these likes: [Thu Jul 29 15:48:29 2010] [error] proxy: FCGI: Got bogus version 66 [Thu Jul 29 15:48:29 2010] [error] (22)Invalid argument: proxy: FCGI: Error dispatching request to : That proxy is then blocked for 60s unless retry=0 has been specified, which can lead to delays in servicing of other requests.
This was fixed some time ago by mod_proxy_fcgi being changed to use a backend connection only once. In the event that an option is added to allow backend connections to be reused, they'll have to be marked for closure after any error to avoid issues like that reported in this bug.
*** Bug 57398 has been marked as a duplicate of this bug. ***