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docs/HyperlinkedInformation/UnderstandingTiming.md
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This document explains useful things about the "Timing" tab. This document explains useful things about the "Timing" tab.
## First, The Warnings ## Be Cautious And Sceptical
There are two issues with the numbers displayed in the "Timing" tab: There are two issues with the numbers:
1. Accurately timing something in the browser is almost 1. Accurately timing something in the browser is almost
a fool's errand. One moment it takes 1ms and the next it a fool's errand. One moment it takes 1ms and the next it
takes 10ms, and you’ll never know why. Noisy. takes 10ms, and you’ll never know why. Noisy.
So, do not ever believe one set of timings numbers. So, don't ever base decision on one set of timings. Run
the same event at least a few of times.
In the future, we'd like to add a 'Run It Again' button, which In the future, we'd like to add a 'Run It Again' button, which
you can click a few times to see if you get stable numbers. you can click a few times to see if you get stable numbers.
@ -17,28 +18,28 @@ There are two issues with the numbers displayed in the "Timing" tab:
2. Don't freak out about any apparent slowness, yet. 2. Don't freak out about any apparent slowness, yet.
You're currently running a dev build, right, not the After all, you're running a dev build, right, not the
production build? production build? And I'm guessing you're also
And I'm guessing you're also running a dev build running a dev build of React?
of React?
Also, using `re-frame-trace` will slow things And using `re-frame-trace` will slow things
down too, what with all that creating and analysing of trace. down too, what with all that creating and analysing of trace.
So, run the production version of your app first before So, run the production version of your app first before
deciding you have a performance problem. Something that deciding you have a performance problem. Something that
takes 100ms in dev might take 20ms in prod. takes 100ms in dev might take 20ms in prod.
This Timing panel is not really about absolute numbers so This Timing Tab is not really about absolute numbers so
much as the relative time taken to do the "parts" of an Epoch. much as the relative time taken to do the different
And, even then, be cautious of these relative numbers because "parts" of an Epoch. Is one View ridiculously slow for some
of point 1 (above). reason, compared to others?
And, even then, remember point 1 (above).
## Know Your Epoch Timeline ## Know Your Epoch Timeline
You'll understand the contents of the Timings tab better if you You'll understand the contents of the Timings tab better if you
understand how an event is processed over time within the browser. understand how an event is processed over time within the browser.
The following infographic might help: The following infographic will help:
<img src="https://raw.githubusercontent.com/Day8/re-frame/master/images/epoch.png"> <img src="https://raw.githubusercontent.com/Day8/re-frame/master/images/epoch.png">