presto-main/src/main/java/io/prestosql/operator/WindowOperator.java/PagesIndexWithHashStrategies/PagesIndexWithHashStrategies
class PagesIndexWithHashStrategies:        PagesIndexWithHashStrategies(
                PagesIndex.Factory pagesIndexFactory,
                List<Type> sourceTypes,
                int expectedPositions,
                List<Integer> preGroupedPartitionChannels,
                List<Integer> unGroupedPartitionChannels,
                List<Integer> preSortedChannels,
                List<Integer> sortChannels)
        {
            this.pagesIndex = pagesIndexFactory.newPagesIndex(sourceTypes, expectedPositions);
            this.preGroupedPartitionHashStrategy = pagesIndex.createPagesHashStrategy(preGroupedPartitionChannels, OptionalInt.empty());
            this.unGroupedPartitionHashStrategy = pagesIndex.createPagesHashStrategy(unGroupedPartitionChannels, OptionalInt.empty());
            this.preSortedPartitionHashStrategy = pagesIndex.createPagesHashStrategy(preSortedChannels, OptionalInt.empty());
            this.peerGroupHashStrategy = pagesIndex.createPagesHashStrategy(sortChannels, OptionalInt.empty());
            this.preGroupedPartitionChannels = Ints.toArray(preGroupedPartitionChannels);
        }