[squid-users] Asynchronous refresh

Hello,

is it possible to refresh/revalidate the squid cache asynchronously?
That means if a client triggers a refresh of an object stored in the cache, could this request be served (with old data) from the cache and the refresh done in the background?

Actually if a refresh happens the client is staled until squid requested all data from the backend.

Why I need this:
The backend could take some time to render the data. On a refresh I don't want that a user have to wait that long.

Workarounds?
http://wiki.squid-cache.org/Features/CollapsedForwarding
Seems quite useful, but using this the first request is still staled during refresh. (According to the docs.)

"Common" workarounds like putting two caches in series seems not useful because the same problem exists. The middle proxy would stale the frontend proxy.

Purging and "warming up the cache" using PURGE + GET reguests is really complex and would not be necessary if the async refreshing would be somehow possible.

Do you know any other caching reverse proxy software that can do that?
I did not test it but from the docs and IRC it seems Varnish, apache Webser, apache Traffic server can't do that and do block on refresh.

Thanks in advance,
Philipp
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Received on Thu Jan 27 2011 - 12:01:00 MST