Re: listen backlog

[ghazel@gmail.com]

On Thu, Dec 2, 2010 at 11:35 PM, Eric Wong <normalperson@yhbt.net> wrote:
> ghazel@gmail.com wrote:
>> On Thu, Dec 2, 2010 at 6:39 PM, Eric Wong <normalperson@yhbt.net> wrote:
>> > ghazel@gmail.com wrote:
>> >> I found this thread
>> >> http://rubyforge.org/pipermail/mongrel-unicorn/2009-September/000031.html
>> >> after googling for the same error located in my nginx error log.
>> >>
>> >> Is there some way to discover the current queue length of the backlog?
>> >> Increasing the maximum size to 2048 "worked" for me as well, but
>> >> obviously clients sit in the queue for a long time. If I could monitor
>> >> queue length I could get some idea of when I have insufficient unicorn
>> >> workers before the delay gets very high or requests fail.
>> >
>> > If you're using Linux, you can use Raindrops[1] to interrogate
>> > via inet_diag or parse /proc/net/{tcp,unix} yourself.
>> >
>> > You can run Raindrops separate/standalone script:
>> > http://git.bogomips.org/cgit/raindrops.git/tree/examples/linux-tcp-listener-stats.rb
>> >
>> > Or use it as middleware (see webpage):
>> > http://raindrops.bogomips.org/
>> >
>> > git clone git://git.bogomips.org/raindrops
>>
>> Amazing! I had somehow never heard of it.
>
> Yeah, I don't have much interest in marketing; that's what users are
> for, but it's a chicken-and-egg problem :x
>
>> I use a unix socket for unicorn (should I not?)
>
> UNIX sockets are faster for nginx <-> Unicorn, but Raindrops is slower
> dealing with them since Linux doesn't export UNIX sockets stats to
> netlink the same way it does for TCP sockets.  So there's always a
> tradeoff :x

When does that netlink speed difference matter - only when collecting stats?

>> so I had to make a copy of
>> linux-tcp-listener-stats.rb to support that. Now I'm able to get stats
>> for my unicorn master
>>
>> However, there seems to be some problem getting stats on TCP sockets:
>>
>> $ ruby linux-tcp-listener-stats.rb 127.0.0.1:9000
>>             address     active     queued
>> linux-tcp-listener-stats.rb:42:in `tcp_listener_stats': Connection
>> refused - sendmsg (Errno::ECONNREFUSED)
>>         from linux-tcp-listener-stats.rb:42
>> $ grep  0100007F:2328 /proc/net/tcp
>>    1: 0100007F:2328 00000000:0000 0A 00000000:00000000 00:00000000
>> 00000000   500        0 25307310 1 ffff880134471700 3000 0 0 2 -1
>>
>> None of the TCP sockets I know to exist seem to work - they all fail
>> with that error.
>
> Odd, which kernel do you have?  You might want to "modprobe inet_diag"
> if you're on an older kernel.  Or you can just comment-out the TCP
> code and use the UNIX sockets code.

Linux hostname 2.6.21.7-2.fc8xen #1 SMP Fri Feb 15 12:34:28 EST 2008
x86_64 x86_64 x86_64 GNU/Linux

Using "modprobe inet_diag" made the script spit out a new error:

            address     active     queued
linux-tcp-listener-stats.rb:42:in `tcp_listener_stats': NLMSG_ERROR
(RuntimeError)
        from linux-tcp-listener-stats.rb:42

$ sudo modprobe -l inet_diag
/lib/modules/2.6.21.7-2.fc8xen/kernel/net/ipv4/inet_diag.ko

I dug in to raindrops a little bit, and it seems the error associated
with the NLMSG_ERROR is -2,
"No such file or directory".


-Greg
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