When to Use ob_flush() and flush() in PHP Output Buffering?

PHP Output Buffers: Ob_Flush() vs. Flush()

Context:
In PHP, output buffering involves capturing and storing data before sending it to the browser. Two key functions in this context are ob_flush() and flush().

Ob_Flush():
ob_flush() flushes the output buffer. This means it explicitly sends the contents of the PHP output buffer to the client. It works on application-issued buffers.

Flush():
flush() flushes the PHP write buffers and the buffers of the underlying system (e.g., CGI, web server). It bypasses application-issued buffers, ensuring that all pending data is sent to the web server.

Why Use Both?
You need to call both ob_flush() and flush() because:

• ob_flush() only affects the application-initiated buffers, while flush() targets the overall output stream.
• PHP itself may also buffer output depending on the backend it uses (e.g., FastCGI). flush() is necessary to send data to the backend.
• Web servers can implement their own buffering mechanisms (e.g., mod_deflate), which flush() can override.

Calling ob_flush() followed by flush() ensures that all data in the output buffers is sent to the client, even if multiple layers of buffering are involved.

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