presto-main/src/main/java/io/prestosql/operator/TableScanWorkProcessorOperator.java/SplitToPages/process
class SplitToPages:        @Override
        public TransformationState<WorkProcessor<Page>> process(Split split)
        {
            if (split == null) {
                return TransformationState.finished();
            }

            checkState(source == null, "Table scan split already set");
            source = pageSourceProvider.createPageSource(session, split, table, columns, TupleDomain::all);
            return TransformationState.ofResult(
                    WorkProcessor.create(new ConnectorPageSourceToPages(aggregatedMemoryContext, source))
                            .map(page -> {
                                processedPositions += page.getPositionCount();
                                recordMaterializedBytes(page, sizeInBytes -> processedBytes += sizeInBytes);
                                return page;
                            }));
        }