sysctl kern.ipc.somaxconn limit 65535 why?
Dan The Man
dan at sunsaturn.com
Wed Jan 4 21:15:11 UTC 2012
On Wed, 4 Jan 2012, Dan The Man wrote:
> On Wed, 4 Jan 2012, Chuck Swiger wrote:
>> On Jan 4, 2012, at 12:44 PM, Dan The Man wrote:
>>>> Even a backlog of a 1000 is large compared to the default listen queue
>>>> size of around 50 or 128. And if you can drain 1000 connections per
>>>> second, a 65K backlog is big enough that plenty of clients (I'm thinking
>>>> web-browsers here in particular) will have given up and maybe retried
>>>> rather than waiting for 60+ seconds just to exchange data.
>>> For web browsers makes sense, but if your coding your own server
>>> application its only a matter of increasing the read and write timeouts
>>> to fill queue that high and still process them.
>> Sure, agreed.
>>> Of course wouldn't need anything that high, but for benchmarking how much
>>> can toss in that listen queue then write something to socket on each one
>>> after connection established to see how fast application can finish them
>>> all, I think its relevant.
>>> This linux box I have no issues:
>>> cappy:~# /sbin/sysctl -w net.core.somaxconn=200000
>>> net.core.somaxconn = 200000
>>> cappy:~# sysctl -w net.ipv4.tcp_max_syn_backlog=20000
>>> net.ipv4.tcp_max_syn_backlog = 200000
>> However, I'm not convinced that it is useful to do this. At some point,
>> you are better off timing out and retrying via exponential backoff than you
>> are queuing hundreds of thousands of connections in the hopes that they
>> will eventually be serviced by something sometime considerably later.
> I agree completely, in practical application this makes sense, but why should
> the OS dictate not being able to temporarily set that setting higher in order
> to fully benchmark the application at 100k+ in the listen queue if the
> developer so chooses? I think that alone should be a good reason, to make
> freebsd developer friendly.
Anyways its not a big deal I can live with a 60k or so benchmark, I just
really wanted to see how freebsd's kqueue would perform processing that
many connections right out of the listen queue.
Dan The Man
CTO/ Senior System Administrator
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Email: Dan at SunSaturn.com
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