Service Times
Table A-11 shows the mean and median service times for different types of requests. The type is taken directly from the fourth field of Squid’s access.log file. The three-digit number following the slash is the HTTP status code. Here I show only 200 (OK) and 304 (Not Modified) replies.
Table A-11. Mean and Median Service Times by Cache Result (IRCache Data)
| Type | Mean (sec) | Median (sec) |
|---|---|---|
| TCP_REFRESH_HIT/200 | 5.165 | 0.281 |
| TCP_MISS/200 | 4.590 | 0.466 |
| TCP_REFRESH_MISS/200 | 4.091 | 0.468 |
| TCP_CLIENT_REFRESH_MISS/200 | 1.889 | 0.215 |
| TCP_HIT/200 | 1.819 | 0.050 |
| TCP_MISS/304 | 1.151 | 0.294 |
| TCP_REFRESH_HIT/304 | 1.107 | 0.219 |
| TCP_IMS_HIT/304 | 0.102 | 0.042 |
The string before the slash indicates how the cache handled the
request. TCP_MISS means the object wasn’t found in the cache at
all. TCP_HIT indicates an unvalidated cache hit. TCP_IMS_HIT
occurs when Squid receives an
If-modified-since request and returns a 304
(Not Modified) reply immediately because the response is fresh
according to the local configuration. TCP_CLIENT_REFRESH_MISS
means that the user-agent sent the no-cache
directive. TCP_REFRESH_HIT occurs when Squid validates its
cached response and learns that the object hasn’t changed. If
the client’s request includes an If-modified-since header, Squid returns the
304 message. Otherwise, it sends the entire object, and the
status is 200. Finally, TCP_REFRESH_MISS means Squid sent
a validation request to the origin server, and the cached
object was out-of-date.
This data is derived from the second field of Squid’s access.log ...