update keep-alive docs

git-svn-id: svn://svn.lighttpd.net/lighttpd/trunk@66 152afb58-edef-0310-8abb-c4023f1b3aa9

doc/performance.txt

@@ -34,13 +34,29 @@ HTTP Keep-Alive
 Disabling keep-alive might help your server if you suffer from a large
 number of open file-descriptors.
 
-::
+The defaults fo the server is: ::
 
   server.max-keep-alive-requests = 128
   server.max-keep-alive-idle = 30
   server.max-read-idle = 60
   server.max-write-idle = 360
 
+handling 128 keep-alive requests in a row on a single connection, waiting 30 seconds
+before a unused keep-alive connection get dropped by lighttpd.
+
+If you handle several connections at once under a high load (let's assume 500 connections
+in parallel for 24h) you might run into the out-of-fd problem described below. ::
+
+  server.max-keep-alive-requests = 4
+  server.max-keep-alive-idle = 4
+
+would release the connections earlier and would free file-descriptors without a to large 
+performance loss.
+
+Disabling keep-alive completly is the last choice if you are still short in filedescriptors: ::
+
+  server.max-keep-alive-requests = 0
+
 Event Handlers
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