topic Re: Server Time vs TTFB in Real User Monitoring

Server Time vs TTFB

edmund_kueh — Mon, 22 Nov 2021 11:43:53 GMT

In this particular example, the server time is 0.1s while TTFB is 0.5s. Why is there a discrepancy between server time and TTFB ? Shouldn't server time equivalent to TTFB ?

ttfb.png

Re: Server Time vs TTFB

JamesKitson — Tue, 02 Jan 2018 16:04:13 GMT

Server time is going to be the time spent receiving the request and creating and sending the response back to the client on the server side. Time to first byte is going to be the time from when the request is sent from the client to when the first byte of the response is received from the server - so this will include transport/network time.

So TTFB should always be higher than the server time.

James

Re: Server Time vs TTFB

edmund_kueh — Tue, 02 Jan 2018 22:34:37 GMT

@James K

Thanks for your reply.

Nevertheless, there can be scenario where TTFB is equal to server time. Does this mean in this case, the transport time/network time is negligible ?

Re: Server Time vs TTFB

JamesKitson — Wed, 03 Jan 2018 14:29:09 GMT

I suppose it's possible that in a very low latency environment that they will be nearly equal. They might appear the same after being rounded but there will always be some transport time.

Re: Server Time vs TTFB

AlexanderSommer — Thu, 04 Jan 2018 13:47:33 GMT

These metrics are based on the W3C navigation timings, so please take also a look at: https://www.w3.org/TR/navigation-timing/#processin...

TTFB is equal to response start
Server time is calculated by: TTFB - request start

Please look also at: What are the exact definitions of the Action Duration Contributors?

Please, let me know if that helps.

Re: Server Time vs TTFB

edmund_kueh — Fri, 05 Jan 2018 01:09:14 GMT

@ Alexander S.

Good stuff. It helps.

From the formula above, it is clear that TTFB > Server time.

Secondly, am I right to say that the network consumption formula below includes time to redirect, time to resolve the DNS and time to establish the TCP connection ?

Network consumption: (requestStart - actionStart) + (responseEnd - responseStart)