[squid-users] time based range_offset_limit

[Alex Rousskov]

On 07/12/2016 02:08 PM, joe wrote:

>>> collapsed_forwarding on

> this is good if you have other client downloading on same time same file it
> has nothing to do with multi connection to the same  ip only it will help
> saving you example if you have 10 client downloading at the same time same
> file so one download it will be.. not 10 download

collapsed_forwarding does not look at client IPs or even connections.
The feature collapses requests based on request URLs. If Squid gets N
more-or-less simultaneous requests for the same URL, then N-1 of those
requests will be "collapsed", subject to certain other conditions(*).

It is rare for the same client to send N concurrent requests for the
same URL, so, in practice, collapsed_forwarding is mostly about multiple
clients a.k.a. "flash crowds".

Said that, some special clients do send concurrent *Range* requests for
the same URL! If Squid receives N concurrent Range requests for the same
URL, I believe Squid will try to collapse them, possibly with disastrous
results, especially if Squid does not strip the Range header when
forwarding a request. Somebody should test that and [at least] file a
bug report if there is indeed a Range request collapsing bug.


HTH,

Alex.
P.S. (*) There are several special conditions that determine whether
Squid will collapse a request. For example, Squid will not collapse a
request if Squid thinks that the future response will not be cachable.