presto-main/src/main/java/io/prestosql/operator/index/StreamingIndexedData.java/StreamingIndexedData/loadNextPage
class StreamingIndexedData:    private boolean loadNextPage()
    {
        Page nextPage = extractNonEmptyPage(pageBuffer);
        while (nextPage == null) {
            if (driver.isFinished()) {
                return false;
            }
            driver.process();
            nextPage = extractNonEmptyPage(pageBuffer);
        }
        currentPage = nextPage;
        return true;
    }