The field stats api returns field level statistics such as lowest, highest values and number of documents that have at least one value for a field.
An api like this can be useful to explore a data set you don't know much about. For example you can figure at with the lowest and highest response times are, so that you can create a histogram or range aggregation with sane settings.
This api doesn't run a search to figure this statistics out, but rather use the Lucene index look these statics up (using Terms class in Lucene). So finding out these stats for fields is cheap and quick.
The min/max values are based on the type of the field. So for a numeric field min/max are numbers and date field the min/max date and other fields the min/max are term based.
Closes#10523
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