Relationship between PHP-CGI process CPU100 % and file_get_contents function

Sometimes, running Nginx, PHP-CGI (php-fpm) Web service Linux server, suddenly the system load increases, use the top command to view, many php-cgi process CPU usage is close to 100%. Later, I found through tracking that the appearance of such cases is closely related to the file_get_contents () function of PHP. Large and medium-sized websites

Sometimes, running Nginx, PHP-CGI (php-fpm) Web service Linux server, suddenly the system load increases, use the top command to view, many php-cgi process CPU usage is close to 100%. Later, I found through tracking that the appearance of such cases is closely related to the file_get_contents () function of PHP.

HTTP-based API calls are common for large and medium-sized websites. PHP programmers like to use the simple and convenient file_get_contents ("http://example.com/") function to get the returned content of a URL, but if the http://example.com/this site responds slowly, file_get_contents () it will remain there and will not time out.

We know that in php. in ini, max_execution_time can be used to set the maximum execution time of PHP scripts. However, this parameter does not take effect in php-cgi (php-fpm. Which of the following parameters in the php-fpm.conf configuration file can really control the maximum execution time of PHP scripts:

 
 

  
  
The timeout (in seconds) for serving a single request after which the worker process will be terminated    
  
  
Should be used when 'max_execution_time' ini option does not stop script execution for some reason    
  
  
'0s' means 'off'    
  
  
  0s    
 
 

The default value is 0 seconds. that is to say, the PHP script will be executed continuously. In this way, when all php-cgi processes are stuck in the file_get_contents () function, the Nginx + PHP WebServer can no longer process new PHP requests, nginx returns "502 Bad Gateway" to the user ". Modify this parameter to set the maximum execution time of a PHP script. For example, if file_get_contents () is changed to 30 s, and the webpage content is slow to be obtained, this means that 150 php-cgi processes can only process 5 requests per second, webServer is also difficult to avoid "502 Bad Gateway ".

To achieve a thorough solution, can only let PHP programmers get rid of the habit of using file_get_contents ("http://example.com/"), but slightly modify, add a timeout time, use the following methods to implement http get requests. If you are in trouble, you can encapsulate the following code into a function.

 
 

  
  
 
  
  
$ Ctx = stream_context_create (array (
  
  
'Http' => array (
  
  
'Timeout' => 1 // set a timeout time, in seconds
  
  
)
  
  
)
  
  
);
  
  
File_get_contents ("http://example.com/", 0, $ ctx );
  
  
?>
 
 

Of course, this is not the only reason for the CPU 100% of the php-cgi process. so, how can we determine it is caused by the file_get_contents () function?

First, run the top command to view the php-cgi process with high CPU usage.

 
 

  
  
top - 10:34:18 up 724 days, 21:01,  3 users,  load average: 17.86, 11.16, 7.69 
  
  
Tasks: 561 total,  15 running, 546 sleeping,   0 stopped,   0 zombie 
  
  
Cpu(s):  5.9%us,  4.2%sy,  0.0%ni, 89.4%id,  0.2%wa,  0.0%hi,  0.2%si,  0.0%st 
  
  
Mem:   8100996k total,  4320108k used,  3780888k free,   772572k buffers 
  
  
Swap:  8193108k total,    50776k used,  8142332k free,   412088k cached 
  
  
  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND                                                            
  
  
10747 www       18   0  360m  22m  12m R 100.6 0.3    0:02.60 php-cgi                                                            
  
  
10709 www       16   0  359m  28m  17m R 96.8  0.4    0:11.34 php-cgi                                                            
  
  
10745 www       18   0  360m  24m  14m R 94.8  0.3    0:39.51 php-cgi                                                            
  
  
10707 www       18   0  360m  25m  14m S 77.4  0.3    0:33.48 php-cgi                                                            
  
  
10782 www       20   0  360m  26m  15m R 75.5  0.3    0:10.93 php-cgi                                                            
  
  
10708 www       25   0  360m  22m  12m R 69.7  0.3    0:45.16 php-cgi                                                            
  
  
10683 www       25   0  362m  28m  15m R 54.2  0.4    0:32.65 php-cgi                                                            
  
  
10711 www       25   0  360m  25m  15m R 52.2  0.3    0:44.25 php-cgi                                                            
  
  
10688 www       25   0  359m  25m  15m R 38.7  0.3    0:10.44 php-cgi                                                            
  
  
10719 www       25   0  360m  26m  16m R  7.7  0.3    0:40.59 php-cgi 
 
 

Find the PID of one of the php-cgi processes with CPU 100% and run the following command to trace the PID:

 
 

  
  
strace -p 10747 
 
 

If the screen displays:

 
 

  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
  
  
select(7, [6], [6], [], {15, 0})        = 1 (out [6], left {15, 0}) 
  
  
poll([{fd=6, events=POLLIN}], 1, 0)     = 0 (Timeout) 
 
 

The problem is caused by file_get_contents.