If you wanted to copy over the mongo database using mongos oplog, how would you do it? Suppose we start copying the database at time T and we finish the copying at time U. We have to read from the oplog from time T onward and apply oplog changes (which also may have been applied between time T and U). Do the oplog transactions have timestamps in them so we can discard records before time T? Are the operations idempotent if we apply them twice (because we are applying an operation already executed between time T and U)? Guess I am confused how to get the initial data before reading from the oplog to continue the real time updates.
