[squid-users] simultanous requests: collapsed_forwarding

Amos Jeffries squid3 at treenet.co.nz
Thu Sep 5 11:00:18 UTC 2019

On 5/09/19 9:52 pm, fansari wrote:
> In our scenario it might/will happen that clients will request the same
> resources simultaneously.
> I ran a test where I start one download with curl and with short delay
> (about 1s) I request the same content by another client.
> 1567673769.781  12123 xxx.xxx.0.1 TCP_MISS/200 15553655 GET
> https://xxx/1.mp4 - HIER_NONE/- video/mp4
> 1567673769.782  13992 xxx.xxx.0.239 TCP_MISS/200 15553655 GET
> https://xxx/1.mp4 - HIER_DIRECT/xxx.xxx.xxx.xxx video/mp4
> From the documentation I found that there is a setting called
> "collapsed_forwarding" which when enabled gives the behaviour we want to
> achieve: let the first request finish with download and then handle the
> others from squid cash.

Not quite, collapsing does not let the first request complete. It starts
sending to all waiting clients as soon as it has response data to
deliver them.

> Since our scenario is not time critical this would be the behaviour we want.
> I am just wondering about one thing: I did not enable this setting (I also
> tried to set it to "off" explicitly) and nevertheless it already behaves
> this way.
> When I interpret the logs correctly the first line indicates a waiting and
> the second shows the download.

I agree, that is what it looks like. The request that finished+logged
first (by 0.001 seconds) took 0.2 seconds less time and did not involve
server contact (HIER_NONE), yet was a "MISS".

> With "collapsed_forwarding on" it behaves in the same way as with "off". To
> me it looks like as if the collapsing is used regardless whether it is
> enabled or not.

Looks to me like you may have found a bug. What exact version of Squid
are you using? (output of "squid -v" please).

If you are using an older Squid can you try the latest v4 and/or
development version to see if the odd behaviour still happens?


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