for (Map.Entry<String, IdMap> e : dos.entrySet()) {
DBCollection dbc = db.getCollection(e.getKey());
IdMap m = e.getValue();
IdMapIterator li = m.iterator();
while (li.hasNext()) {
li.advance();
long oid = li.value();
if (oid == -1) {
//the document has been inserted and then deleted again
//do not save time of insertion
continue;