Subset Mode
You can enable subset mode in MongoDB Charts to restrict the input
collection to 1000 randomly selected documents. To enable subset
mode, use the Subset toggle in the Preview
section. The Subset toggle for a chart doesn't persist when
the chart renders on a dashboard. So, if you enable subset mode when
you build a chart, the data that renders in the dashboard isn't sampled.
Note
When you enable subset mode and you specify a filter, MongoDB Charts takes the sample of 1000
documents before it applies the filter. So, MongoDB Charts might use
fewer than 1000 documents to plot the chart.
Use Case
Consider using subset mode when you draft a chart and heavily modify chart options. In this situation, subset mode lets the chart render quickly during the building process. When you feel satisfied with your chart, save it as soon as possible.
Note
Due to the random nature of sampling, when you have subset mode enabled, your visualizations might change each time the chart loads in the chart builder.