我知道这是一个老问题，但我想把我的答案写下来给视觉学习者。我在万维网上找不到任何解释输出缓冲的图表，所以我自己在Windows mspaint.exe中做了一个图表。

如果输出缓冲被关闭，那么echo将立即向浏览器发送数据。

如果打开了输出缓冲区，那么echo会在将数据发送到浏览器之前将数据发送到输出缓冲区。

phpinfo

要查看输出缓冲是否打开/关闭，请参考核心部分的phpinfo。output_buffering指令将告诉你Output buffering是否打开/关闭。

在本例中，output_buffering值为4096，这意味着缓冲区大小为4 KB。它还意味着在Web服务器上打开了输出缓冲。

php . ini

可以通过改变output_buffering指令的值来打开/关闭和改变缓冲区大小。只需在php.ini中找到它，将其更改为您选择的设置，并重新启动Web服务器。你可以在下面找到我的php.ini示例。

; Output buffering is a mechanism for controlling how much output data
; (excluding headers and cookies) PHP should keep internally before pushing that
; data to the client. If your application's output exceeds this setting, PHP
; will send that data in chunks of roughly the size you specify.
; Turning on this setting and managing its maximum buffer size can yield some
; interesting side-effects depending on your application and web server.
; You may be able to send headers and cookies after you've already sent output
; through print or echo. You also may see performance benefits if your server is
; emitting less packets due to buffered output versus PHP streaming the output
; as it gets it. On production servers, 4096 bytes is a good setting for performance
; reasons.
; Note: Output buffering can also be controlled via Output Buffering Control
;   functions.
; Possible Values:
;   On = Enabled and buffer is unlimited. (Use with caution)
;   Off = Disabled
;   Integer = Enables the buffer and sets its maximum size in bytes.
; Note: This directive is hardcoded to Off for the CLI SAPI
; Default Value: Off
; Development Value: 4096
; Production Value: 4096
; http://php.net/output-buffering
output_buffering = 4096

指令output_buffering并不是唯一关于输出缓冲的可配置指令。你可以在这里找到其他可配置的输出缓冲指令:http://php.net/manual/en/outcontrol.configuration.php

例如:ob_get_clean ()

下面你可以看到如何捕获一个回声，并在将它发送到浏览器之前对它进行操作。

// Turn on output buffering  
ob_start();  

echo 'Hello World';  // save to output buffer

$output = ob_get_clean();  // Get content from the output buffer, and discard the output buffer ...
$output = strtoupper($output); // manipulate the output  

echo $output;  // send to output stream / Browser

// OUTPUT:  
HELLO WORLD

示例:Hackingwithphp.com

更多关于输出缓冲区的示例信息可以在这里找到:

http://www.hackingwithphp.com/13/0/0/output-buffering

PHP使用输出缓冲来提高性能并执行一些技巧。

您可以让PHP将所有输出存储到缓冲区中，并一次性输出所有输出，从而提高网络性能。 在某些情况下，您可以访问缓冲区内容而无需将其发送回浏览器。

想想这个例子:

<?php
    ob_start( );
    phpinfo( );
    $output = ob_get_clean( );
?>

上面的示例将输出捕获到一个变量中，而不是将其发送到浏览器。默认情况下，Output_buffering是关闭的。

当您希望在发送内容后修改标头时，可以使用输出缓冲。

想想这个例子:

<?php
    ob_start( );
    echo "Hello World";
    if ( $some_error )
    {
        header( "Location: error.php" );
        exit( 0 );
    }
?>

Web开发人员的输出缓冲，初学者指南:

Without output buffering (the default), your HTML is sent to the browser in pieces as PHP processes through your script. With output buffering, your HTML is stored in a variable and sent to the browser as one piece at the end of your script. Advantages of output buffering for Web developers Turning on output buffering alone decreases the amount of time it takes to download and render our HTML because it's not being sent to the browser in pieces as PHP processes the HTML. All the fancy stuff we can do with PHP strings, we can now do with our whole HTML page as one variable. If you've ever encountered the message "Warning: Cannot modify header information - headers already sent by (output)" while setting cookies, you'll be happy to know that output buffering is your answer.

这是对php输出缓冲的总结。(XAMPP php.ini)

Output buffering is a mechanism for controlling how much output data (excluding headers and cookies) PHP should keep internally before pushing that data to the client. If your application's output exceeds this setting, PHP will send that data in chunks of roughly the size you specify. Turning on this setting and managing its maximum buffer size can yield some interesting side-effects depending on your application and web server. You may be able to send headers and cookies after you've already sent output through print or echo. You also may see performance benefits if your server is emitting less packets due to buffered output versus PHP streaming the output as it gets it. On production servers, 4096 bytes is a good setting for performance reasons.

注意:输出缓冲也可以通过输出缓冲控制来控制 功能。

可能的值:

On =启用，缓冲区不受限制。(请谨慎使用)

关=禁用

Integer =启用缓冲区，并以字节为单位设置缓冲区的最大大小。

注意:这个指令对于CLI SAPI是硬编码为Off的

默认值:关闭

开发价值:4096

产值:4096

http://php.net/output-buffering output_buffering = 4096

顾名思义，这里的内存缓冲区用于管理脚本的输出如何出现。

这里有一个关于这个主题的很好的教程

2019年更新。如果你有专用服务器和SSD或更好的NVM, 3.5GHZ。你不应该使用缓冲来让加载速度更快的网站在100 -150毫秒。

由于网络比2019年使用性能服务器(服务器，内存，磁盘)和打开APC PHP处理脚本慢，生成脚本有时只需要70ms，另一次仅是网络需要时间，从10ms到150ms从位于用户服务器。

所以如果你想要快150ms，缓冲就会变慢，因为需要额外的缓冲数据收集，这会产生额外的成本。10年前，当服务器制作1s脚本时，它很有用。

请小心output_buffering有限制，如果你想使用jpg加载它会自动刷新和崩溃发送。

欢呼。

你可以制造快速的河流 或 你可以安全地做tama:)