presto-main/src/main/java/io/prestosql/operator/ScanFilterAndProjectOperator.java/ScanFilterAndProjectOperator/processPageSource
class ScanFilterAndProjectOperator:        WorkProcessor<Page> processPageSource()
        {
            return WorkProcessor
                    .create(new ConnectorPageSourceToPages(pageSourceMemoryContext))
                    .yielding(yieldSignal::isSet)
                    .flatMap(page -> pageProcessor.createWorkProcessor(
                            session.toConnectorSession(),
                            yieldSignal,
                            outputMemoryContext,
                            page,
                            avoidPageMaterialization))
                    .transformProcessor(processor -> mergePages(types, minOutputPageSize.toBytes(), minOutputPageRowCount, processor, localAggregatedMemoryContext))
                    .withProcessStateMonitor(state -> memoryContext.setBytes(localAggregatedMemoryContext.getBytes()));
        }