what's the difference between proxy_store and proxy_cache?

[zhenwei]

>From Nginx official site there are two method to store remote upstream
on local file system, "proxy_cache" and "proxy_store", the document
describes clearly on how to configure, but still I have problem on the
differences. Months ago I did some test over the both and found
proxy_cache owns far better performance, and I thought proxy_cache is
"cache in memory", recently after diving into source code, I recognized
both are file based, so i'm not sure if it could afford high connection
where disk probably becomes the bottleneck.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,218263,218263#msg-218263