Nginx Why not use "deferred" on nginx server block listen line?

rdan · Apr 10, 2015

Like this:
Code:
server {
    listen 80 default_server deferred;
    server_name www.phcorner.net;
Any disadvantages I'm not aware of "deferred" ?

eva2000 · Apr 10, 2015

trial and error test for yourself

rdan · Apr 10, 2015

Haha, seems just a very little info about it.
So leave it off for now.

rdan · May 24, 2015

TCP_DEFER_ACCEPT can help boost performance by reducing the amount of preliminary formalities that happen between the server and client.
What does the deferred option mean in NGINXs listen directive? - Stack Overflow

eva2000 · May 24, 2015

try it and see

linux - Real-World Use of TCP_DEFER_ACCEPT? - Unix & Linux Stack Exchange

rdan · May 24, 2015

Haha, sure I will

eva2000 · May 24, 2015

from linux - Real-World Use of TCP_DEFER_ACCEPT? - Unix & Linux Stack Exchange

The three-way handshake that they are refering to is part of the TCP connection establishment, the option in question doesn't relate specifically to this. Also note that data exchange is not part of the three way handshake, this just creates the TCP connection in the open/established state.

Regarding the existance of this option, this is not the traditional behaviour of a socket, normally the socket handler's thread is woken up when the connection is accepted (which is still after the three way handshake completes), and for some protocols activity starts here (e.g. an SMTP server sends a 220 greeting line), but for HTTP the first message in the conversation is the web browser sending its GET/POST/etc line, and until this happens the HTTP server has no interest in the connection (other than timing it out), thus waking up the HTTP process when the socket accept completes is a wasteful activity as the process will immediately fall asleep again waiting for the necessary data.

While there is certainly argument that waking up idle processes can make them 'ready' for further processing (I specifically remember waking up login terminals on very old machines and having them chug in from swap), but you can also argue that any machine that has swapped out said process is already making demands on its resources, and making further unnecessary demands might overall reduce system performance - even if your individual thread's apparent performance improves (which it also may not, an extremely busy machine would have bottlenecks on disk IO which would slow other things down if you swapped in, and if its that busy, the immediate sleep might swap it right back out). It seems to be a gamble, and ultimately the 'greedy' gamble doesn't necessarily pay off on a busy machine, and certainly causes extra unnecessary work on a machine that already had the process swapped in - your approach optimises for a machine with a large memory set of processes that are mostly dormant, and swapping one dormancy for another is no big deal, however a machine with a large memory set of active processes will suffer from extra IO, and any machine that isn't memory limited, suffers, any CPU bound machine will be worse off.

My general advice regarding that level of performance tuning would be to not make programatic decisions about what is best anyway, but to allow the system administrator and operating system to work together to deal with the resource management issues - that is their job and they are much better suited to understanding the workloads of the entire system and beyond. Give options and configuration choices.

To specifically answer the question, the option is beneficial on all configurations, not to the level you'd ever likely notice except under an extreme load of HTTP traffic, but it's theoretically the "right" way to do it. It's an option because not all Unix (not even all Linux) flavours have that capability, and thus for portability it can be configured not to be inclided.
Click to expand...

rdan · May 27, 2015

I'm still confuse whether this is useful to enable .

rdan · May 27, 2015

Hard to understand via google translate :/
Re: deferred и bind и много виртуальных хостов

rdan · May 28, 2015

Take advantage of TCP/IP options to optimize data transmission - TechRepublic

I just enable it in port 80 and 443 .

rdan · Feb 27, 2022

rdan said: ↑

deferred
Click to expand...

I'm still confused until now if it's really worth to have this enabled .

eva2000 · Feb 27, 2022

rdan said: ↑

I'm still confused until now if it's really worth to have this enabled .
Click to expand...

Test and see

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