[APM] x-axis on the instance bubble chart is broken

[nehaduggal]

Versions: Kibana: 7.12

Issue:

In the new Instance scatter plot chart, the x-axis looks empty and so off with just 1 data point. In the attached screenshot you can see that the instances tpm is 7.6tpm but it looks like the dot is on 0 making it super confusing. We should have some more even interval labels on the x-axis and not show anything with a non 0 tpm as a 0 value.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[sorenlouv]

What should we use as the domain (aka range) for the x-axis in this example? imo the ideal domain in this case is [0, 16] which would put the instance in the middle. But the logic to find the upper ound might be odd, something like:

Math.max(median_throughput * 2, maxThroughput)

Other options is simply [0, 7.6] as we normally do. This would place the instance at the very right end of the plot.

[elasticmachine]

Pinging @elastic/datavis (Feature:ElasticCharts)

[elasticmachine]

Pinging @elastic/datavis (Team:DataVis)

[markov00]

This current behavior is caused by the fact that you are using a linear scale with a dataset that has only 1 single value.
The auto computed domain is basically [7.6,7.6] and matching that to the range (width of the chart) basically renders the chart as in the screenshot.

We can improve that and move the point to the center in this specific case (see elastic/elastic-charts#1095), but in the meantime, as @sqren proposed, adding a fixed domain can fix that. Another workaround for this specific use case it to use the Ordinal scale type for the x-axis instead of the linear, only when you have a single data point. with that, the point will be positioned in the middle of the chart.