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Mike Thompson 2018-01-18 12:31:14 +11:00
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docs/HyperlinkedInformation/UnchangedLayer2.md
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@ -1,4 +1,3 @@
## Unchanged Layer 2 Subscriptions
This document briefly explains why `re-frame-trace` gives you an option to
ignore unchanged layer 2 subscriptions.
@ -14,7 +13,7 @@ between `layer 2` and `layer 3` subscriptions:
- `layer 3` subscriptions take values from `layer 2` nodes as inputs, and
compute a materialised view of those values. Just to repeat: they never directly
extract values from `app-db`. They create new values where necessary, and because of it
they to do more serious CPU hogging work. So we never want to run
they to do more serious CPU work. So we never want to run a
`layer 3` subscriptions unless it is necessary.
This structure delivers efficiency. You see, **all** (currently instantiated) `layer 2` subscriptions
@ -27,19 +26,18 @@ propagation of values through the signal graph will be pruned.
The more computationally intensive `layer 3` subscriptions, and ultimately
the views, will only recompute if and when there has been a change in their data inputs.
We don't want your app recomputing views only to find that nothing has changed.
We don't want your app recomputing views only to find that nothing has changed. Inefficient.
### Back To Tracing
Because `layer 2` subs run on every single modification of `app-db`, and because
very often nothing has changed, their trace can be a bit noisy.
Yes, it happened, but it just isn't that interesting.
very often nothing has changed, their trace can be a bit noisy. Yes, it happened,
but it just isn't that interesting.
So `re-frame-trace` gives you the option of filtering out trace for
the `layer 2` subscriptions where the value this time is the same as the
value last time.
the `layer 2` subscriptions where the value "this time" is the same as the
value "last time".
On the other hand, if a `layer 2` subscription runs and its value is
different to last time, that's potentially fascinating and ypou'll want to
different to last time, that's potentially fascinating and you'll want to
be told all about it. :-)