Introducing the method of using php output_buffering cache

buffer is a memory address space. The default size of the Linux system is generally 4096 (4kb). It is mainly used to store data transfer areas between devices with unsynchronized speeds or devices with different priorities.

Using buffer can reduce the waiting time between processes.

For example, when you open a text editor and enter a character, the system does not write it to disk immediately. Instead, it is stored in a buffer. When a buffer is full, the contents of the buffer will be written to the disk.

Of course, you can also use flush to force the buffer data to be written to disk.

In php, such as echo, print, the output is not immediately passed to the browser for output through tcp. Instead, the data is written to php buffer. When a php buffer is full, it will be passed to the browser through tcp.

echo /print -> php output_buffer -> tcp buffer -> browser

php output_buffering

By default, php buffer is turned on, and the default value is 4096 (4kb). The output_buffering configuration can be found in php.ini. It will not be sent to the browser until the buffer is full.

You can also set ob_start(), so that even if it exceeds the default value (4kb), it will not be sent to the browser immediately. It will not be sent to the browser until the script is completed or the ob_end_flush method is called. Output to browser.

1.output_buffering=4096, output less data (less than one buffer)

<?php
for($i=0; $i<10; $i++){
    echo $i.&#39;<br>&#39;;
    sleep(2);
}
?>

Running result : Wait until all scripts are completed before outputting, because the data is not full of one buffer size.

2.output_buffering=4096, output less data (less than one buffer), turn off output_buffering, modify output_buffering=0 in php.ini

<?php
for($i=0; $i<10; $i++){
    echo $i.str_repeat(" ",500).&#39;<br>&#39;; // 当接受到的256(甚至更多)个字节以后才开始显示该页面，所以必须发送一些额外的空格来让这些浏览器显示页面内容。
    flush();
    sleep(1);
}
?>

Run results: Because php buffering is disabled, there is no need to wait for the script to run before it can be output. The data does not stay in the php buffer, and you can see intermittent output. echo -> tcp buffer ->browser

3. When output_buffering=4096, output larger data (larger than one buffer), do not use ob_start()

<?php
for($i=0; $i<10; $i++){
    echo file_get_contents(&#39;f.txt&#39;).$i.&#39;<br>&#39;;
    sleep(1);
}
?>

Run result: f.txt is a file larger than 4kb. Because it is larger than the default value of the buffer, the buffer space is not enough. Whenever a buffer is full, it will be output, so Intermittent output can be seen.

4. When output_buffering=4096, to output larger data (larger than one buffer), use ob_start()

<?php
ob_start();
for($i=0; $i<10; $i++){
    echo file_get_contents(&#39;f.txt&#39;).$i.&#39;<br>&#39;;
    sleep(1);
}
?>

Running results: Because ob_start() is used, a large enough space will be set for the buffer, so it will be saved until the script is executed and then output.

output_buffering method

1.ob_start
Activate the output_buffering mechanism , once activated, the script is no longer output directly to the browser, but is temporarily written to the PHP buffering area. It is not sent until the script has finished running.

2.ob_get_contents
Get the data in php buffering. Note: it must be called before ob_end_clean(), otherwise you will only get null characters.

3.ob_end_flush and ob_end_clean
ob_end_flush will output the data in php buffering, but will not clear it.
ob_end_clean will not output, but will only clear the data in php buffering.

Note:
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...In fact, they operate on different objects. In some cases, flush does nothing at all.ob_* series of functions operate the output buffer of PHP itself.So , ob_flush is to refresh PHP's own buffer.And flush, strictly speaking, this only has an actual effect when PHP is installed as an Apache Module (handler or filter). It refreshes the WebServer (It can be considered to refer specifically to apache) buffer.Under the sapi of apache module, flush will indirectly call apache's api by calling the flush member function pointer of sapi_module: ap_rflush refreshes apache's output buffer, Of course, the manual also says that there are some other modules of Apache that may change the result of this action.Some Apache modules, such as mod_gzip, may perform output caching by themselves, which will cause the flush() function to The results produced are not immediately sent to the client browser. Even the browser will cache the received content before displaying it. For example, the Netscape browser caches content until it receives a newline or the beginning of an html tag, and does not display an entire table until it receives a tag. Some versions of Microsoft Internet Explorer will only begin to display the page after receiving 256 bytes, so some additional spaces must be sent to allow these browsers to display the page content.

#So, the correct order to use the two is. First ob_flush, then flush.
Of course, under other sapi, you can not call flush. However, in order to ensure the portability of your code, it is recommended to use it together.

This article explains how to use php output_buffering cache. For more related content, please pay attention to the php Chinese website.

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