[tor-talk] exit node cache

[jiang song]

when a Tor client send a http request, requesting a lot of data, like
picture, files or video
the http request will finally be sent by a Tor exit node,
and the coresponding web server will respond to the Tor exit node with http
response carrying the large bulk data.
The bulk data is transmitted via tcp connection between the tor exit node
and the webserver,
so there will be a lot of TCP ACKs.

my understanding is:
Since the Tor exit node may spend a bit more time to send the http data
back to the Tor client,

1) if the Tor exit node is continueing acknowledging the webserver on
receipt of tcp segments,
then the Tor exit node will have to cache a lot data, is it right?
or
2) actually the TCP ack is from the Tor client? if the Tor exit node
doesn't receive the TCP ack from the Tor client,
it will never acknowledge the receipt of tcp segments from the webserver?

which understanding is right?
thanks!