presto-main/src/main/java/io/prestosql/operator/AssignUniqueIdOperator.java/AssignUniqueIdOperator/generateIdColumn
class AssignUniqueIdOperator:    private Block generateIdColumn()
    {
        BlockBuilder block = BIGINT.createFixedSizeBlockBuilder(inputPage.getPositionCount());
        for (int currentPosition = 0; currentPosition < inputPage.getPositionCount(); currentPosition++) {
            if (rowIdCounter >= maxRowIdCounterValue) {
                requestValues();
            }
            long rowId = rowIdCounter++;
            verify((rowId & uniqueValueMask) == 0, "RowId and uniqueValue mask overlaps");
            BIGINT.writeLong(block, uniqueValueMask | rowId);
        }
        return block.build();
    }