Sunday, January 1, 2012

A use case for SPDY header compression

A use case for SPDY header compression:

380 bytes of gzipped javascript (550 uncompressed), sent with 8.8KB of request cookies and 5.5KB of response cookies. That overhead is bad enough to mess with TCP CWND defaults - which means you are taking multiple round trips on the network just to move half a KB of js. For HTTP, that's a performance killer! Those cookies are repeated almost identically on every transaction with that host.

SPDY's dedicated header contexts and the repetitive nature of cookies means those cookies can be reduced ~98% for all but the first transaction of the session. Essentially the cookies remain stateless for app developers, along with the nice properties of that, but the transport leverages the connection state to move them much more efficiently.