Clarify latency-vs-service-time FAQ #1133
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Thank you for this clarification! This topic pops up frequently and I think a more engineering/factual explanation wrt how Rally builds the request traffic actually helps.
I left a comment, mostly for discussion; after all I think, for the sake of keeping the explanation simple, we should just stick to target-throughput as done in this PR.
docs/faq.rst
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| generate and send the next request. In this mode ``latency`` and | ||
| ``service_time`` are identical. | ||
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| * **Throughput-throttled mode**: You may prefer to run benchmarks with a target |
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Internally Rally uses a concept called "Schedule". There are different ways to alter the traffic that Rally generates by issuing requests:
- target-throughput (in requests/sec)
- target-interval (inverse of target-throughput i.e. amount of secs to wait per request)
- use poisson distribution or a custom schedule of your own
As all of those actually end up influencing the schedule that Rally will use to issue requests, I wonder if we should be talking about the schedule here briefly and adjust wording below, e.g. in line 51/52 instead of "according to this target" "according to the schedule".
However ... I think this concept is tricky by itself and by trying to provide a very generic answer (as I suggest) we might be confusing the reader, whereas the description in this PR is easier to understand by using a concrete example (via target throughput). @danielmitterdorfer WDYT?
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Ack, thanks for the clarification. I'll try and generify the wording and maybe link to the schedule docs if I can work out how.
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I pushed some more generic words in 18ae7f2 which I don't think make it any more complicated.
I tried to work out how to cross-reference the docs on the schedule bit of a track but timed out after a couple of minutes of trying to understand what on earth the Sphinx docs were trying to tell me. A cross-ref on the first occurrence of the word schedule would be very helpful IMO, could someone else push an update that adds one?
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could someone else push an update that adds one?
@DaveCTurner I've added one; it's available if you merge the latest master into your branch. You can use it as follows:
:ref:`your custom link text here <track_choose_schedule>`
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Thanks @danielmitterdorfer, done in 4f999a7.
With this commit we add a new label to the section that explains a schedule in Rally so it can be referenced in other parts of the docs. Relates #1133
I found the answer to the FAQ on latency vs service time unclear. It doesn't really define what
latencymeans in throughput-throttled mode, and I'm not sure I fully understand the analogy it uses. I'm opening this to propose some alternative words, based on my interpretation of the previous answer, but I wouldn't be surprised if I'm still misunderstanding the details.