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Cache Not Utilized
If the le cache is not utilized, your server is not performing optimally. Since most sites have lots
of GIF or JPEG les that should always be cacheable, you need to use your cache eectively.
Some sites, however, do almost everything through CGIs, SHTML, or other dynamic sources.
Dynamic content is generally not cacheable, and inherently yields a low cache hit rate. Don’t be
too alarmed if your site has a low cache hit rate. The most important thing is that your response
time is low. You can have a very low cache hit rate and still have very good response time. As
long as your response time is good, you might not care that the cache hit rate is low.
Check your hit ratio using statistics from perfdump, the Admin Console Monitoring tab, or
wadm stats commands. The hit ratio is the percentage of times the cache was used with all hits to
your server. 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.
In addition, if you are doing a lot of CGI or NSAPI calls, you might have a low cache hit rate. If
you have custom NSAPI functions, you might also have a low cache hit rate.
Keep-Alive Connections Flushed
A web site that might be able to service 75 requests per second without keep-alive connections
might be able to do 200-300 requests per second when keep-alive is enabled. Therefore, as a
client requests various items from a single page, it is important that keep-alive connections are
being used eectively. If the KeepAliveCount shown in perfdump (Total Number of
Connections Added, as displayed in the Admin Console) exceeds the keep-alive maximum
connections, subsequent keep-alive connections are closed, or “ushed,” instead of being
honored and kept alive.
Check the KeepAliveFlushes and KeepAliveHits values using statistics from perfdump or the
Number of Connections Flushed and Number of Connections Processed under Keep Alive
Statistics on the Monitoring Statistics page. For more information, see
“Keep-Alive
Information” on page 53
.
On a site where keep-alive connections are running well, the ratio of KeepAliveFlushes to
KeepAliveHits is very low. If the ratio is high (greater than 1:1), your site is probably not
utilizing keep-alive connections as well as it could.
To reduce keep-alive ushes, increase the keep-alive maximum connections (as congured on
the conguration'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
connections open.
Keep-AliveConnections Flushed
Chapter3 • CommonPerformanceProblems 87