The graph shows the number of concurrent outgoing connections present in the proxy server.

The majority of the connections are due to misses. A hit may require an outgoing connection to verify the freshness of an object.

Proxy connect time is the time it takes to send an HTTP request to a server. A proxy may request a document from the original server or another proxy. In case of a local hit for an "old" object, a proxy may send an If-Modified-Since request. Note that IP lookup activity is not included in proxy connect time. For this graph, we ignore requests that did not contact other servers.

Why does it take longer for [future] hits to connect?

The graph plots the distribution of proxy connect time during peak load.

This experiment measures the time it takes to receive a reply from the original server or another proxy after a request has been sent.

Hit replies are much "faster" than misses. This may be attributed to a small size of a hit reply: a reply can be recorded as a hit only if it is a 304 or Not-Modified reply. 304 replies contain only a small header and no document content. Also, the remote server does not have to read the document from disk to send a 304 reply. Thus, the server may reply "faster".

See also server reply time versus file size experiment.

Server reply time depends on the size of the reply. Here we plot this dependency. Variations in reply time for large files are due to insufficient number of such files that leads to less stable median.

Note that reply time of a hit does not depend on a document size. This is because the only possible reply for a hit is a 304 reply, and all 304 replies have approximately the same [small] size regardless of the size of the corresponding document.

Server response time is the total time it takes to send a request and receive a reply from a primary server. In other words, it is the sum of connect and reply times.