D.2 General Comments

I show, for each test, how the sustainable throughput varies over time. The y-axis shows the throughput (responses per second). The x-axis is the ratio of fill-traffic volume to cache size . Because each test takes a different amount of time, this is a nice way to normalize all the results. The test is over when the cache has been filled twice.

In most traces, you'll see that sustainable throughput decreases over time. At the beginning of the test, the throughput is very high. Here, the disks are empty, and Squid doesn't need to replace old objects. The throughput for a full cache is usually worse than for an empty cache. This is a common characteristic of proxy benchmarks and emphasizes the importance of reaching steady-state conditions. Don't be fooled by impressive results from short tests.

The Throughput, Response Time, and Hit Ratio values given in the summary tables are taken from the last 25% of the test. Here, between 1.5 and 2.0 on the x-axis, the throughput is more or less stable and flat. I report the mean of the throughput, response time, and hit ratio values in this range from the trace data.

Throughput is the most interesting metric in these tests. It is given in responses per second. The rows in each summary table are sorted by throughput.

The response time numbers are less interesting because they are all about the same. I decided to report them to show that, indeed, the results stay within the response time window defined by the workload. The target response time is around 1.5 seconds, but the actual response time varies depending on the particular test.

The response hit ratio values are also not particularly interesting. The ideal hit ratio for this workload is about 58%. Due to an as-yet unresolved Polygraph bug, however, the hit ratio decreases slightly as the test progresses.

Keep in mind that these results are meant to demonstrate the relative performance of different options, rather than the absolute values. You'll get different numbers if you repeat the tests on different hardware.