MongoDB WiredTiger use clustered index on _id field?

Question

I know MongoDB WiredTiger use clustered index to store data. Is WiredTiger use clustered index on _id field or another key generate by WiredTiger？

Answer 1

WiredTiger uses a binary tree-like structure to store documents. It is a basic key-value store, where the key is an internally generated identifier, and the value is the document.

All indexes, including the one on the _id field, map field values to the internal identifier.