Setting default row_limit to 50K for line chart

[michellethomas]

This PR sets default row_limit to null for line chart, bar chart, compare chart, and area chart. Because row_limit is a new field on timeseries charts, existing charts may be affected if they have over 10,000 rows.

@mistercrunch what do you think about setting the row_limit default to null? We could also set the default to 50,000 instead, it seems less likely that a chart with 50,000 rows would render very well anyways.

[mistercrunch]

I think we should put some upper limit as people can crash their browser if they don't. The upper limit should be lower than the number at which we know the browser will crash for sure. This may vary quite a bit based on the viz type, number of series, ...

I also think we should allow users to crash their browsers if they want to clear or bump up the limit. They might know something we don't know, have a quantum computer or something.

Notice that the label that shows the number or rows in the explore view should turn yellow and warn "you've reached the limit" to make sure users knows that data is missing. We may want to bring more attention to this and have a clear tooltip that explains the tradeoffs.

[mistercrunch]

[mistercrunch]

Here, I've been meaning to do this for a while #6252

[codecov-io]

Codecov Report

Merging #6244 into master will decrease coverage by 0.1%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6244      +/-   ##
==========================================
- Coverage   76.85%   76.74%   -0.11%     
==========================================
  Files          47       47              
  Lines        9393     9393              
==========================================
- Hits         7219     7209      -10     
- Misses       2174     2184      +10

Impacted Files	Coverage Δ
superset/db_engine_specs.py	54.91% <0%> (-0.85%)	⬇️
superset/connectors/sqla/models.py	80% <0%> (-0.75%)	⬇️

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[michellethomas]

Sounds good thanks Max. I did some testing on what the upper limit should be for different viz types, I think the only one we should increase is the line chart, I set it to 50000. This is still pretty slow but usable. The bar chart and area chart get pretty slow at 10K, they could be a little larger but this seems fine. The compare chart doesn't have a way of hiding the legend so there's no chance anyone is using it even at 10K currently.

[mistercrunch]

+1