presto-main/src/main/java/io/prestosql/operator/TableScanWorkProcessorOperator.java/TableScanWorkProcessorOperator/getUpdatablePageSourceSupplier
class TableScanWorkProcessorOperator:        Supplier<Optional<UpdatablePageSource>> getUpdatablePageSourceSupplier()
        {
            return () -> {
                if (source instanceof UpdatablePageSource) {
                    return Optional.of((UpdatablePageSource) source);
                }
                return Optional.empty();
            };
        }