Why using $all in mongodb is much slower?

Question

I asked a similar question before Why $in is much faster than $all? and the answer is the idea that $in (that scan more row and return more result) should be faster due to sorti

Answer 1

This is working as designed as answered in Why $in is much faster than $all? as answered.

$all with only one item is equivalent with normal search right?

No, it is a different codepath and different operator.

MongoDB explains the difference here. $all matches all values as opposed to any (which $in does). There are further usage examepls here.

The relevant SERVER ticket that you want is here. You can vote on this ticket.