In a build failure on MongoDB master, we observed the following behavior:
- There is a validation failure on the local.replset.initialSyncId collection. That collection is unusual in a few different ways:
- It is an immediately durable (journaled) collection.
- It only ever has a single document in it.
- Writes to the collection are not done at a timestamp.
- The validation failure tends to happen shortly after startup, and results in either the value in the collection or index not being found by the validation.
- The document and its index are inserted as part of a single WiredTiger transaction, so they should either both be visible or neither - that's a guarantee that WiredTiger gives, which is not being honored here.