[support] Understanding why authcache issues ajax requests

[Dan Kegel]

I'm slowly coming up the Drupal performance learning curve.
APC and MySQL query cache were easy.  autcache is a bit
more challenging.

I'm trying to understand authcache.  I turned it on,
not bothering with memcache, and after I realized that
you can't test it (easily?) with apachebench, started
playing with it interactively.  Seems to work great
except that Authcache Debug says it's making ajax
requests, and I can't figure out why.  In the following
example, I opened page node/251 (by its long name),
then clicked on Authcache Debug to see what it said:

Authcache.info (logged in: joe)page_render: "1437.65 ms"
page_queries: "366 queries @ 516.49 ms (36%)"
cache_render: "2.07 ms (69,352% increase)"
cache_uid: "2"
cache_inc: "database"
cache_time: 1389502279
node_author: "admin"
(page_age): "17 seconds"
Disable caching for this browser session
HTML/JavaScript time: 99 ms
________________________________
Authcache.ajaxRequest #1
Request:q: "node/251"
node_history: "251"
Response:node_history: "1389502279"
db_queries: "2 queries @ 55.2 ms"

Any clue as to how to figure out why it's making that ajax request?

Thanks,
Dan