Reactivity performance

[jg10-mastodon-social]

This is an elaboration issue prompted by #193 (comment)

There is a need for development of performance assessment, measurement, testing and potentially optimisation particularly for the implementation of reactivity from the global RDF store to component rendering updates.

[jg10-mastodon-social]

Copying from #193 (comment) regarding use of debounceTime

I consider debounceTime to be a potentially buggy heuristic. What we want to know is that there will not be in any more emissions that would cause a rerender. I've set the time rather conservatively at 250ms. This is probably too long because it's latency that a user might notice, but on a slow device the user impact of rerendering could be worse. I expect we'll want to reduce the time but would want some evidence to support the selection of a new value.

So my preference was to avoid debounceTime if an argument can be made to do so. Relations are the workhorse of RDF, so we expect them to change frequently and for groups to be updated at once when documents are loaded. They're also used frequently across the user interface so potentially have a big effect on rerendering (my early experiments had some very painful churn). Types are updated infrequently and are used less frequently in the user interface. I expect the first set of types to be already loaded in the store when first called, so emissions are likely to be one at a time when changes are made. It therefore felt safe to avoid the debounceTime for observeTypes