Open loop vs. Closed loop Clients

[SunnyRaj]

httperf is probably a closed loop - a quick google search says it will be a closed loop only if no timeout is specified. Closed loop will have high latency which in turn will lower the throughput due to longer wait times. In our experiments we do specify a timeout interval - does that make it an open loop? If so, how?

In any case, it might be worth to test it with a UDP based benchmark like iperf or even memcached UDP based clients. (Ask Yuxin about this).

[SunnyRaj]

It seems that when a timeout is specified in httperf it operates in a open-loop manner. This link in httperf mailing list says "just so you know, if you do not specify a timeout you will be operating in a closed-loop rather than an open loop manner."

[twood02]

a timeout is likely to be on the scale of seconds, so even with a timeout set it will still be a mostly closed loop workload---i.e., within one checkpoint interval if the clients send their max number of open requests then they aren't going to send any more even if the system could handle it (but is just slow to respond because of network buffering).

If we use a more intensive web benchmark (eg the php/sql scripts) this should be less of an issue.