How can I reduce the waiting (ttfb) time

The TTFB is not the time to first byte of the body of the response (i.e., the useful data, such as: json, xml, etc.), but rather the time to first byte of the response received from the server. This byte is the start of the response headers.

For example, if the server sends the headers before doing the hard work (like heavy SQL), you will get a very low TTFB, but it isn't "true".

In your case, TTFB represents the time you spend processing data on the server.

To reduce the TTFB, you need to do the server-side work faster.

I have met the same problem. My project is running on the local server. I checked my php code.

$db = mysqli_connect('localhost', 'root', 'root', 'smart');

I use localhost to connect to my local database. That maybe the cause of the problem which you're describing. You can modify your HOSTS file. Add the line

127.0.0.1 localhost.