presto-main/src/main/java/io/prestosql/operator/index/IndexSnapshotBuilder.java/IndexSnapshotBuilder/reset
class IndexSnapshotBuilder:    public void reset()
    {
        memoryInBytes = 0;
        pages.clear();
        outputPagesIndex = pagesIndexFactory.newPagesIndex(outputTypes, expectedPositions);
        missingKeysIndex = pagesIndexFactory.newPagesIndex(missingKeysTypes, expectedPositions);
    }