Index used but keys & docs examined is 0 with docs returned is around 300

one of my aggregation query using match (a,b), graphlookup and unwind has explain output with index being used (idx_a_1_b_1) shows keys & docs examined is 0 with docs returned is around 300. So, my question is why does the docs and keys examined are 0 event though documents are returned?

Hi @Sateesh_Bammidi welcome to the community!

This is very hard to determine without actual examples, do you mind posting:

Best regards
Kevin