AT:

• I can read about some benchmark how long it takes to get the exact count for :
  • 10 000
  • 50 000
  • 100 000
  • 500 000
  • 1 000 000
  • 5 000 000
    documents

Hint:
There are two possible ways of finding the count:

• use term aggregation and get the exact count
• use client side scrolling to sum up the exact cardinality