We should consider adding a server parameter as limit on the max number of keys to check in a batch on secondaries (independent of batch boundaries), both for extra keys and missing keys checks. This is because if there are many inconsistent entries but we use minKey as the start of the first batch, or maxKey as the end of the last batch, those first/final batches may do a lot of work on the secondaries that the primary may not expect. As a result, this can slow down oplog application.