In-depth understanding of PHP output caching (output_buffering)

In-depth understanding of PHP output caching (output_buffering)_PHP tutorial

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Release： 2016-07-21 15:07:09

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First clarify the output order of PHP
1. Turn on the php output cache: echo,print -> php output_buffring -> server buffering -> browser buffering -> browser display
2. PHP output cache is not turned on: echo,print -> server buffering -> browser buffering -> browser display

Also make it clear The browser's output cache: 256Bytes for IE, 1000Bytes for Chrome and FireFox. Only when the output data reaches this length or the script ends, the browser will output the data on the page

Let’s talk about the use Several PHP settings and APIs:
1.output_buffering configuration in php.ini
•Off: means turning off the PHP output cache
•On: turning on the infinite output cache
• 4096: Open the output cache with a size of 4096 Byte

2.php.ini in the implicit_flush configuration
•On: Indicates that flush is automatically called after each output (such as echo, print) () function, directly output
•Off: Contrary to On, flush() will not be called after each output, and it will not be output until the server buffering is full, but we can use the flush() function instead. It doesn’t matter if it is turned on, it is more flexible

3.ob_flush() function: Take out the data in PHP buffering and put it into server buffering

4.flush() function: Take out Server buffering The data is put into browser buffering

5.ob_start() function: I don’t know much about this function now, because the output will not be clear after it is turned on. Controlled by ob_flush(), even if ob_flush() and flush() are used, the data cannot be output immediately on the browser. What is known now is that if output_buffering=Off, even if ob_start() is used, the output data cannot be cached , and if output_buffering=On, even if ob_start() is not used, the output data can be cached by PHP, so I think ob_start is relatively useless, so I will ignore it for the time being

Then let’s look at the code (setting output_buffering= 4096,implicit_flush=Off)

Copy code The code is as follows:

,1000); //IE cache 256Bytes
echo str_repeat(' ', 1000); Save it instead of directly outputting
for($i=0;$i<5;$i++) {
echo $i.'
';
ob_flush();
flush();
sleep(1);
}
?>

The output result of the code here is output line by line. For the specific principle, please refer to the efficacy of the ob_flush() and flush() functions.
If any of these two functions is missing, under my setting, it will wait until 0 , 1, 2, 3, 4 are all cached and then output together
Finally, I quote a paragraph from Laruence’s blog, I hope it will be helpful to everyone’s understanding

The description of ob_flush/flush in the manual is to refresh the output buffer, and it also needs to be used in conjunction, so it will cause confusion to many people...

Actually, they operate on different objects. In some cases, flush does nothing at all..

The ob_* series of functions operate the output buffer of PHP itself.

So, ob_flush is to refresh PHP's own buffer.

Strictly speaking, flush only has an actual effect when PHP is installed as an apache Module (handler or filter). It refreshes the buffer of the WebServer (which can be considered specifically apache).

Under the sapi of apache module, flush will indirectly call the apache api by calling the flush member function pointer of sapi_module: ap_rflush refreshes the output buffer of apache. Of course, the manual also says that there are some other modules of apache. It may change the result of this action..
1. Some Apache modules, such as mod_gzip, may perform output caching by themselves,
2. This will cause the results generated by the flush() function to not be immediately cached. Sent to client browser.
3.
4. Even the browser will cache the received content before displaying it. For example, Netscape
5. The browser will cache the content until it receives a newline or the beginning of the html tag, and the entire table will not be displayed until
6. it receives the tag.
7.
8. Some versions of Microsoft Internet Explorer will only start displaying the page after receiving 256
9. bytes, so some extra spaces must be sent to make this
10. Some browsers display page content.
So, the correct order of using the two is. First ob_flush, then flush,
Of course, under other sapi, you can not call flush, just to ensure that your code For portability, it is recommended to use it together.