[YBA] TCP connection rate

[Gilad Ben-Yossef]

Jonathan Ben Avraham wrote:

> Hi Marc,
> The .NET client has a bug that prevents use of persistent MySQL 
> connections. The application is already cached up the wazoo.
>
> Where would I look in the kernel to see if it is rejecting the 
> connections as opposed to MySQL? Or is this just unlikely given that 
> the hardware is fairly robust?

I don't know of a way to get the statistics from the kernel for that, 
but maybe this will help:

"The duration that affects the rate at which new connections are 
accepted is the time spent on the queue of pending incoming connections. 
This duration is equal to the round trip time for the SYN|ACK message 
and its ACK response plus the time taken for the client to process the 
SYN|ACK message plus the delay for the server to process the ACK and 
call *accept()*.

The rate at which new connections can be accepted is equal to the number 
of entries which can fit on the listen queue divided by the average 
length of time each entry spends on the queue. Therefore, the larger the 
queue, the greater the rate at which new connection requests can be 
accepted."


http://www.linuxjournal.com/files/linuxjournal.com/linuxjournal/articles/023/2333/2333s2.html

> Thanks,
>
>  - yba
>
>
> On Mon, 2 Feb 2009, marc at swiftouch.com wrote:
>
>> Date: Mon, 2 Feb 2009 18:28:21 +0200 (IST)
>> From: marc at swiftouch.com
>> To: Jonathan Ben Avraham <yba at tkos.co.il>
>> Cc: Gilad Ben-Yossef <gilad at codefidence.com>, ILUG 
>> <linux-il at cs.huji.ac.il>
>> Subject: Re: [YBA] TCP connection rate
>>
>> Hi all
>>
>> Without delving into the stack behaviour, I would try the 
>> (potentially) cheaper route - is there a possibility of amalgamating 
>> queries to the database, thereby reducing the per second metric? Or - 
>> perish the thought (caveat emptor, I am not acquainted with the app) 
>> - caching replies at the client?
>>
>> I am not sure the netstat trick can work in this case - both since 
>> (as YBA noted) the connexions are brief and because netstat deals 
>> with connections very late in their lifecycle. I am not sure how 
>> connexions pending on the stack would show up.
>>
>> M
>>
>> ---MAV
>> Marc. Volovic
>> +972-54-467-6764
>> marc at swiftouch.com
>> Sent from my iPhone
>>
>> On Feb 2, 2009, at 5:06 PM, Jonathan Ben Avraham <yba at tkos.co.il> wrote:
>>
>>> Hi Gilad,
>>> Thanks. The problem is that the connections are exceedingly 
>>> short-lived. By the time I type in "netstat -na" already 1000 of 
>>> them have come and gone.
>>>
>>> - yba
>>>
>>>
>>> On Mon, 2 Feb 2009, Gilad Ben-Yossef wrote:
>>>
>>>> Date: Mon, 02 Feb 2009 16:29:23 +0200
>>>> From: Gilad Ben-Yossef <gilad at codefidence.com>
>>>> To: Jonathan Ben Avraham <yba at tkos.co.il>
>>>> Cc: ILUG <linux-il at cs.huji.ac.il>
>>>> Subject: Re: [YBA] TCP connection rate
>>>> Jonathan Ben Avraham wrote:
>>>>
>>>>> Dear list members,
>>>>> What limits the rate that the Linux kernel TCP stack can accept 
>>>>> new connections? How is that rate related to the rate that the 
>>>>> application listening on a port can handle the connections? That 
>>>>> is, if I try to connect and get ECONNREFUSED is there a way for me 
>>>>> to know if I got it because the kernel could not handle the 
>>>>> connection rate or if I got it because I had more connection 
>>>>> attempts than the backlog parameter of my listen() call? In other 
>>>>> words, do I need to tune the kernel or the application (MySQL) for 
>>>>> the desired high connection rate and how would I know?
>>>>
>>>> Just check what the value of the backlog parameter is and then use 
>>>> netstat to watch the application connections when you get 
>>>> ECONNREFUSED error. If the number of connections in netstat is 
>>>> equal (or at least very close to) the backlog parameter then it's 
>>>> the backlog parameter, otherwise it's something else.
>>>>
>>>> Gilad
>>>>
>>>>
>>>
>>> -- 
>>> EE 77 7F 30 4A 64 2E C5  83 5F E7 49 A6 82 29 BA    ~. .~   Tk Open 
>>> Systems
>>> =}------------------------------------------------ooO--U--Ooo------------{= 
>>>
>>>    - yba at tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -
>>>
>>> _______________________________________________
>>> Linux-il mailing list
>>> Linux-il at cs.huji.ac.il
>>> http://mailman.cs.huji.ac.il/mailman/listinfo/linux-il
>


-- 
Gilad Ben-Yossef 
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Codefidence Ltd.
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