Cache Not Utilized
Ifthe le cache is not utilized, your server is not performing optimally. Since most sites have lots
ofGIF or JPEG les that should always be cacheable, you need to use your cache eectively.
Somesites, however, do almost everything through CGIs, SHTML, or other dynamic sources.
Dynamiccontent is generally not cacheable, and inherently yields a low cache hit rate. Don’t be
tooalarmed if your site has a low cache hit rate. The most important thing is that your response
timeis low. You can have a very low cache hit rate and still have very good response time. As
longas your response time is good, you might not care that the cache hit rate is low.
Checkyour hit ratio using statistics from perfdump, the Admin Console Monitoring tab, or
wadmstats commands. The hit ratio is the percentage of times the cache was used with all hits to
yourserver. A good cache hit rate is anything above 50%. Some sites might even achieve 98% or
higher.For more information, see “File Cache Information (Static Content)” on page 59.
Inaddition, if you are doing a lot of CGI or NSAPI calls, you might have a low cache hit rate. If
youhave custom NSAPI functions, you might also have a low cache hit rate.
Keep-Alive Connections Flushed
Aweb site that might be able to service 75 requests per second without keep-alive connections
mightbe able to do 200-300 requests per second when keep-alive is enabled. Therefore, as a
clientrequests various items from a single page, it is important that keep-alive connections are
beingused eectively. If the KeepAliveCount shown in perfdump (Total Number of
ConnectionsAdded, as displayed in the Admin Console) exceeds the keep-alive maximum
connections,subsequent keep-alive connections are closed, or “ushed,”instead of being
honoredand kept alive.
Checkthe KeepAliveFlushes and KeepAliveHits values using statistics from perfdump or the
Numberof Connections Flushed and Number of Connections Processed under Keep Alive
Statisticson the Monitoring Statistics page. For more information, see “Keep-Alive
Information”on page 53.
Ona site where keep-alive connections are running well, the ratio of KeepAliveFlushes to
KeepAliveHitsis very low. If the ratio is high (greater than 1:1), your site is probably not
utilizingkeep-alive connections as well as it could.
Toreduce keep-alive ushes, increase the keep-alive maximum connections (as congured on
theconguration's Performance Tab ⇒HTTP sub tab or the wadm set-keep-ailve props
command).The default value is 200. By raising the value, you keep more waiting keep-alive
connectionsopen.
Keep-AliveConnections Flushed
Chapter3 • Common Performance Problems 87