Varnish Storage API

[Stephan Richter]

On Wednesday, July 14, 2010, Poul-Henning Kamp wrote:
> If that happens, there isn't really anything you can do about it, because
> the delay will be disk-I/O which will also hit your MC/HTTP process.

I understand. I thought that would be the answer but did not want to lead to 
the answer through my question. 

> Without knowing how big your object set/hot set size is, it is hard to
> predict what the actual pattern will be.

Unfortunately we do not know that either yet. But it will be in the order of 
1k clients asking for video stream data (such as Smooth Streaming or similar 
HTTP-based video streams). There will be, let's say, 100 channels to watch. 
Data only has to be kept for a few seconds (since it is live streaming), so 
thats roughly 500-1000MB of cached files. Of course each client will usually 
only access one stream at a time.

> What happens if a client asks for an object the varnish does not have ?

It will fetch it from the backend and the driver request will get the already 
cached version. So there is a definite fail-safe there. In addition of pre-
populating the Varnish cache, the driver makes sure that the data is picked up 
from the backend, so that the backend's memory footprint is controlled. I much 
rather have Varnish worry about cache and memory management. :-)

Regards,
Stephan
-- 
Entrepreneur and Software Geek
Google me. "Zope Stephan Richter"