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Whats the proper definition of TTFB or Time to First Byte? Different tools seem to have different definitions of it.

Some call TTFB the time from the request got sent to the first byte (post TCP connection established) and others include DNS and Connect times in TTFB.

So my question really is does it include DNS, Connect, and Send, or does it exclude them?

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It is the duration from the virtual user making an HTTP request to the first byte of the page being received by the browser. This time is made up of the socket connection time, the time taken to send the HTTP request and the time to taken to get the first byte of the page.

This actually measures performance/throughput penalty while processing/transmitting some overhead data: HTTP headers, TCP headers, control information, checksums, etc.

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what abt DNS Lookup, is that included? Also where did you find this definition? – Webly Nov 13 '09 at 20:40
"making an HTTP request" does not include it: TTFB is used when benchmarking a WEBSERVER, not the whole WWW ;) You won't believe: it was wikipedia :) – kolypto Nov 14 '09 at 1:02

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