[erlang-questions] HTTP requests and the meaning of eaddrinuse

[Oscar Hellström]

Sverker Eriksson wrote:
> Johnny Billquist wrote:
>   
>> Sverker Eriksson wrote:
>>     
>>> Johnny Billquist wrote:
>>>       
>>>> [...] you will most probably hit the limit of the number of open 
>>>> file descriptors long before you exhaust all the local port numbers. 
>>>> By default on on my mac, the max file descriptors is 256 (per 
>>>> process). There is also a limit on the total number of file 
>>>> descriptors in the OS. Nowhere near the theoretical limit of 65536 
>>>> ports in tcp. So that should give you enfile or emfile. 
>>>>         
>>> The internal TIME_WAIT state of the TCP protocol may cause exhaustion 
>>> of port numbers even though the file descriptor limit is much lower 
>>> than 65536. Use the netstat command tool to view lingering 
>>> connections in TIME_WAIT state.
>>>       
>> True, if the connections aren't closed properly.
>>     
> Actually, kind of the opposite. The peer that actively closes the 
> connection by calling close() will cause its "socket" into TIME_WAIT. 
> It's like a quarantine to avoid late arriving packets of the old 
> connection from being confused with a new connection using the same 
> port. A major flaw of TCP if you ask me.
>   
And I case of put, the inets HTTP client will close the connection after
the response is received, since it is mixing up pipelining and keep
alive []. We have seen this during load tests of our systems, in which
case we implemented interface pools to get around the problem.
>> But yes, that could be it. I wonder if eaddrinuse really is returned 
>> in that case. [...]
>>     
> I experienced this some time ago writing a benchmark on Linux. I'm quite 
> sure it was eaddrinuse that I got when the port numbers where exhausted.
>
>
> /Sverker
>
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