Theoretical connections/second limit using Varnish
Michael S. Fischer
michael at dynamine.net
Wed Apr 29 18:36:00 CEST 2009
On Apr 29, 2009, at 9:30 AM, Nick Loman wrote:
> Michael S. Fischer wrote:
>> On Apr 29, 2009, at 9:22 AM, Poul-Henning Kamp wrote:
>>> In message <49F87DE4.3040300 at loman.net>, Nick Loman writes:
>>>> Has Varnish got a solution to this problem which does not involve
>>>> time-wait recycling? One thing I've thought of is perhaps
>>>> is used or could be used when Varnish makes connections to the
>>> Varnish tries as hard as reasonable to reuse backend connections,
>>> so you should be able to get multiple requests per backend
>>> If this is not the case for you, you should find out why backend
>>> are not reused.
> Hi Poul-Henning, Michael,
> I've configured Apache with KeepAlive off, so I expect the TCP
> connection to be closed after each request and Varnish won't be able
> to use it.
> I've done that for a specific reason relating to backend PHP
I don't dispute your reasoning; my employer does this as well.
KeepAlive with Apache/PHP can be a recipe for resource starvation on
your origin servers.
> I typically have thousands of connections in TIME_WAIT mode as a
> result, which is expected, but I wonder what the solution could be
> if I ever hit more connections than local ports available.
I think SO_REUSEADDR is the answer - I'm somewhat surprised that
Varnish doesn't set it by default for the backend connections.
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