Varnish Dirty Caching

Damien Wetzel dwetzel at
Tue Jul 3 12:33:17 CEST 2007

Hello all,

when working for speedera, we use to have the ability to define
two time-out timers in the config: timer1 and timer2

timer1 would define the time to receive the TCP ack of the http
request to the backend. (or something equivalent)

timer2 the time to receive the first chunk of http data

upon completion of one of these timers we could configure the caches
to say :
1) serve stale content
2) serve a user defined static html page or null gif image
3) redirect the requests to a backup backend.

with savvis we had a variable called Background Refresh Mode when
positionned on a URL would make the cache serve the content
immediatly when it becomes staled and then the cache would (try to) make
the refresh in the background.


Poul-Henning Kamp writes:
 > In message <20070702211450.GA16119 at falcon>, Christoph writes:
 > >i'd like to implement dirty-caching using varnish.
 > I'm busy twisting the variable visibility in VCL into proper shape
 > right now, and that will move us a bit closer to what your want
 > to do.
 > The critical question is how we define "backend is down" and how
 > fast and efficient we can detect it.
 > Ideas for how to express it in VCL are very welcome.
 > -- 
 > Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
 > phk at FreeBSD.ORG         | TCP/IP since RFC 956
 > FreeBSD committer       | BSD since 4.3-tahoe    
 > Never attribute to malice what can adequately be explained by incompetence.
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