When determining if a query is eligible for the express path, we check for the presence of an _id index, which requires going to the catalog and iterating through the index list. Later, we retrieve the _id index again, this time to actually execute the query.

To improve perf for queries using the _id index in the express path, we should see if it's possible to avoid the double iteration. One way to do this could be to pass the _id index descriptor down to the express plan from the get_executor code.