Re: [squid-users] How does Squid prevent stampeding during a cache miss?

david robertson wrote:
> Squid 2.x supports this:
>
> # TAG: collapsed_forwarding (on|off)
> # This option enables multiple requests for the same URI to be
> # processed as one request. Normally disabled to avoid increased
> # latency on dynamic content, but there can be benefit from enabling
> # this in accelerator setups where the web servers are the bottleneck
> # and reliable and returns mostly cacheable information.
>
> It's exactly what you're looking for. Basically it causes Squid to
> request the URL from the origin server one time, and serves the other
> requests the stale content.
>

If stampeeding is a worry the stale-if-error and stale-while-revalidate
Cache-Control: options would also be useful (sent from the origin web
server). These are supported by 2.7.

  They prevent a stampeed if the collapsed request itself fails or a
group of clients waiting have to be broken out of the collapsed bunch
(ie different Vary: requirements).

  The way stale-while-revalidate works is designed specifically for
stampeeds. So can also be used for a good result even without collapsed
forwarding. Though best result is when combined.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE9 or 3.1.5