get profiling back to perceived "magical"

[hamilton]

Profiling has gotten much slower since May. I think there are some easy solutions to this.

1. it would be nice if we re-ordered the queue a bit. Right now, we enqueue a bunch of stuff that the user doesn’t need to see immediately (such as top ns). I’m noticing that profiling feels a lot. slower with the new numeric histogram rug plot. It would feel faster if that was the lowest-priority item in the priority queue. So I’m thinking of the following priorities:

• SummaryProfile – anything that is directly visible in the profiling, e.g. the initial histograms, null counts, cardinality
• EssentialProfileDetails – top Ns, timestamp viz
• DeeperProfileDetails – things like the rug plot, which seem to take a bit longer to run.

2. Along with that, we could prefetch a detail if the user mouses over the profile. This would amount to re-prioritizing the details to be "UserRequestedProfile", which should be above SummaryProfile here. @domoritz suggests also taking a look at premonish, which uses some simple heuristics to determine if a user's mouse is moving toward a DOM element. This would buy us another 200ms to reorder the priority queue, which would likely make it so that the detail views are already calculated.

[hamilton]

We're going to stick to keeping to (1) for this sprint.

[domoritz]

Makes sense. Doing the magic prefetching only gives you marginal benefits and everything else needs to be right first.