private void handleSummary(DocumentSummary ds) {
        int summaryCount = ds.getSummaryCount();
        log.log(Level.FINE, () -> "Got DocumentSummary with " + summaryCount + " summaries for query with selection " +
                                  params.getDocumentSelection());
        synchronized (summaryMap) {
            for (int i = 0; i < summaryCount; i++) {
                DocumentSummary.Summary summary = ds.getSummary(i);
                summaryMap.put(summary.getDocId(), summary);
            }
        }
    }
A visitor data handler that performs a query in a content cluster with the
searchvisitor visitor plugin. It collects and merges hits (sorted
descending on rank), summaries (sorted on document id), and
groupings. The resulting data can be fetched when the query has
completed.

@author Ulf Carlin
container-search/src/main/java/com/yahoo/vespa/streamingvisitors/StreamingVisitor.java