Details of proxy caching for Google App Engine?

Question

The Google App Engine must have some kind of reverse caching proxy, because when I set the Cache-Control public, max-age=300 response header Cache-Control public, max-age=300 from one of my servlets, subsequent requests to the application engine appear in the logs as follows: /testcaching 204 1ms 0cpu_ms 49kb , while non-cached appear in the logs as: /testcaching 200 61ms 77cpu_ms 49kb .

Anyway, my question is: are there any details about this reverse caching proxy?

Answer 1

Some of the details that would be nice to have answers to are:

http://code.google.com/p/googleappengine/issues/detail?id=2258#c3

Answer 2

The best documentation I've found about the App Engine cache proxy is a post to the App Engine group . The relevant parts are given below for posterity. All loans are owned by Brandon Wirtz:

"If you want the cache cache to work, you need to make sure that you have completed the following steps.

• Set publication. If you do not install the publication, it will not be cached.
• Set the maximum age. If you installed publicly, but did not specify max-age, it will not be cached.
• Use a comma. public, max-age=300 working fine. Public; max-age=300 Public; max-age=300 no.
• Set the age to over 60. 61 seems to be caching. 60 no. There will probably be some volume that I will cache based on expiration, but 61 seconds in the volumes we start 61 seems to be cached, and 60 never seems to be.
• Set the age to less than 366 days. 364 days seems to work. 365 works the most. 366 never works. So those are “Expire never” kinds of messages that people talk about versions that never expire. Well, 10 years is not the right answer.
• Expires with a date does not seem to help, and apparently can prevent caching in some cases. I think it could be a drift of hours. Or something about how legible the parser is the date format. Things that work in browsers don't always work correctly in edgecache ... (e.g. Semi versus comma)
• Install both Pragma and Cache-Control. If Pragma is not set to Public, then Cache-Control seems to be ignored. "