why not build file lists in parallel?

[Carlos Carvalho]

It often takes rsync a long time to start transfers because of the
time to build the file lists of a (big) sync in both ends of the
connection. Usually it's not rsync's fault; most of it is spent
waiting for the machine to return stat info.

Version 3 avoids this delay by starting the transfers without waiting
for the complete file lists. However this only happens in two cases:
if version 3 runs in both ends (which is still rare) and no options
such as delay-updates are used. And this is even rarer...

The rsync client first asks for the server to send it the whole file
list, and does nothing during this period; only after having the
sender list it starts to build the local one. Why doesn't it build the
local list while waiting for the server's??? That could speed big syncs
significantly.