public Set<Ack> removeAcknowledged(final String uaid, final Set<Ack> acked) {
final ViewResult viewResult = db.queryView(query(Views.UNACKS.viewName(), uaid));
final List<Row> rows = viewResult.getRows();
final Collection<BulkDeleteDocument> removals = new LinkedHashSet<BulkDeleteDocument>();
for (Iterator<Row> iter = rows.iterator(); iter.hasNext(); ) {
final Row row = iter.next();
final JsonNode json = row.getValueAsNode();
final JsonNode doc = json.get(DOC_FIELD);
final String channelId = doc.get(CHID_FIELD).asText();
for (Ack ack : acked) {
if (ack.getChannelId().equals(channelId)) {
removals.add(BulkDeleteDocument.of(doc));