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Persistent Connections

The previous experiments are based on HTTP 1.0, where a TCP connection is established by clients for each individual request. The HTTP 1.1 specification adds support for persistent (keep-alive) connections that can be used by clients to issue multiple requests in sequence. We modified both versions of Flash to support persistent connections and repeated the previous experiment. The results are shown in Figure 4.

Figure 4: Persistent HTTP

With persistent connections, the request rate for small files (less than 50KBytes) increases significantly with Flash and Flash-Lite, due to the reduced overhead associated with TCP connection establishment and termination. The overheads of the process-per-connection model in Apache appear to prevent that server from fully taking advantage of this effect.

Persistent connections allow Flash-Lite to realize its full performance advantage over Flash at smaller file sizes. For files of 20KBytes and above, Flash-Lite outperforms Flash by up to 43%. Moreover, Flash-Lite comes within 10% of saturating the network at a file size of only 17KBytes and it saturates the network for file sizes of 30KBytes and above.

Peter Druschel