How does sample function work in InfluxDB

Question

I tried to use sample() function in influxDB to get random dataset from it. I want to know more about the internal working of the sample() function present in InfluxDB, like does it scan the whole measurement(table) to get the random subsets from it or it has its own buckets from where it takes the data and provides output? I have tried looking at the official documentation but they do not have a good description of the "sample()" function.