Collections (except if clustered) are required to have an _id index. We have code that detects missing _id index and tries to repair the catalog at startup if missing but we do not have any early enforcement that the catalog entry will be written with the _id index to begin with. Any bug resulting in a missing _id is difficult to fix as it is not allowed to perform catalog writes without timestamp and may result in silent performance degradation if _id lookup is not performant.

We should consider enforcing this property at an earlier stage to minimize the likelihood of corrupt catalog entries as much as possible.