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What is the difference between latency and response time?

I started to read famous Martin Fowler book (Patterns of Enterprise Application Architecture)

I have to mention that I am reading the book translated into my native language so it might be a reason of my misunderstanding.

I found their definitions (back translation into English):

Response time - amount of time to process some external request
Latency - minimal amount of time before getting any response.

For me it is the same. Could you please highlight the difference?

Solution

  • One way of looking at this is to say that transport latency + processing time = response time.

    Transport latency is the time it takes for a request/response to be transmitted to/from the processing component. Then you need to add the time it takes to process the request.

    As an example, say that 5 people try to print a single sheet of paper at the same time, and the printer takes 10 seconds to process (print) each sheet.

    The person whose print request is processed first sees a latency of 0 seconds and a processing time of 10 seconds - so a response time of 10 seconds.

    Whereas the person whose print request is processed last sees a latency of 40 seconds (the 4 people before him) and a processing time of 10 seconds - so a response time of 50 seconds.