Reverse lookup is executed on only the primary.

In reverse lookup, the primary iterates through index table at a given start point until it hits a batch boundary. For each index key traversed in batch:

• Perform a lookup for the record that the index key points to
• If we do not find the record, report the inconsistency to the health log
• Add the size of the index key plus the document to the total count of bytes. If we have exceeded a speed parameter, complete the batch and return