sendfile_max_chunk breaking unbufferred php-fcgi

Floris nginx-forum at nginx.us
Sun Jun 14 13:52:26 UTC 2015


Hi,

I was having the problem that if a single client on the local LAN is
downloading a large static file, the download is effectively monopolizing
nginx, and no other requests are handled simultaneously.
Reading the manual I came across the sendfile_max_chunk option that sounded
like that may fix it:

==
Syntax:    sendfile_max_chunk size;
Default:    sendfile_max_chunk 0;
Context:    http, server, location

When set to a non-zero value, limits the amount of data that can be
transferred in a single sendfile() call. Without the limit, one fast
connection may seize the worker process entirely.
==


However I noticed that if I enable that, PHP scripts running without
buffering suddenly no longer work properly.


nginx.conf:

==
events {
    worker_connections  1024;
}

http {
    include      mime.types;
    default_type application/octet-stream;

    server {
        listen      80;
        server_name $hostname;
        sendfile    on;
        sendfile_max_chunk 8192;

        root /var/www;

        location / {
            index index.php index.html index.htm;
        }

        location ~ \.php$ {
            try_files     $uri =404;

            fastcgi_buffering off;
            fastcgi_pass  unix:/var/run/php-fpm.sock;
            include       fastcgi.conf;
        }
    }
}
==


t2.php for testing purposes:

==
<?php

for ($i = 0; $i < 10; $i++)
{
        echo "test!\n";
        flush();
        sleep(1);
}
==

When retrieving that, the connection stalls after the first flush:

==
$ telnet 192.168.178.26 80
Trying 192.168.178.26...
Connected to 192.168.178.26.
Escape character is '^]'.
GET /t2.php HTTP/1.0

HTTP/1.1 200 OK
Server: nginx/1.6.3
Date: Sun, 14 Jun 2015 13:21:53 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
X-Powered-By: PHP/5.6.9

test!
==

If I remove either the "sendfile_max_chunk 8192;" or "fastcgi_buffering
off;" line it does work, and I do get all 10 test! messages:

==
telnet 192.168.178.26 80
Trying 192.168.178.26...
Connected to 192.168.178.26.
Escape character is '^]'.
GET /t2.php HTTP/1.0

HTTP/1.1 200 OK
Server: nginx/1.6.3
Date: Sun, 14 Jun 2015 13:22:23 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
X-Powered-By: PHP/5.6.9

test!
test!
test!
test!
test!
test!
test!
test!
test!
test!
Connection closed by foreign host.
==

Am I doing something wrong, or is this a bug?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,259603,259603#msg-259603



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