docs: def _collect_indexes_stats(self, instance, db, tags):
          """
          Collect indexes statistics for all collections in the configuration.
          This use the "$indexStats" command.
          """
          for coll_name in instance.get('collections', []):
              try:
                  for stats in db[coll_name].aggregate([{"$indexStats": {}}], cursor={}):
                      idx_tags = tags + [
                          "name:{0}".format(stats.get('name', 'unknown')),
                          "collection:{0}".format(coll_name),
                      ]
                      val = int(stats.get('accesses', {}).get('ops', 0))
                      self.gauge('mongodb.collection.indexes.accesses.ops', val, idx_tags)
              except Exception as e:
                  self.log.error("Could not fetch indexes stats for collection %s: %s", coll_name, e)