Reduce table counts on index page with many databases

[simonw]

Since #467 the index page has attempted to optimistically count times.

My personal Dogsheep has enough connected databases and tables that the page can still take way too long to load - sometimes more than twenty seconds.

[simonw]

The easiest solution would be to only show counts on the index pages for immutable (-i) databases.

I don't like this, because the most common uses of Datasette don't in my opinion justify it. Most of the time Datasette will be running against a single, small, mutable database. I'd like to show counts in that case.

Some options:

• disable counts on the index page for mutable databases of more than one is attached
• disable counts on the index page for databases where the file in disk is larger than a specified threshold (maybe 10MB? I'm making up this number)
• implement an overall timer which cuts off table counting once the sum of time spent on it has gone beyond a second

Worth prototyping a bit to see what works best.

[simonw]

I tried this out in 34bc16a with an upper limit of 100MB and it worked an absolute treat against my personal Dogsheep.