Method AddNode

be/src/scheduling/hash-ring.cc:43–69

}

void HashRing::AddNode(const IpAddr& node, std::string_view scheduling_seed_in) {
  // This node should not already be in the set.
  std::pair<NodeIterator, bool> node_pair = nodes_.insert(node);
  // 'second' tells whether a new element was inserted. It must be true.
  DCHECK(node_pair.second) << "Failed to add: " << node;
  NodeIterator node_it = node_pair.first;
  // If the scheduling seed argument is empty, use the IP address
  std::string_view scheduling_seed = scheduling_seed_in;
  if (scheduling_seed.empty()) scheduling_seed = node;
  uint32_t hash = HashUtil::Hash(scheduling_seed.data(), scheduling_seed.length(), 0);
  // Generate multiple hashes for the node by using the hash as a seed to a PRNG.
  pcg32 prng(hash);
  for (uint32_t i = 0; i < num_replicas_; i++) {
    uint32_t hash_val = prng();
    // Check for hash collision
    auto hashmap_it = hash_to_node_.find(hash_val);
    // Write this new value if:
    // 1. There is no hash collision.
    // -OR-
    // 2. There is a hash collision, but the underlying IpAddr is less than
    //    the current value.
    // This guarantees consistency regardless of the order of adds and removes.
    if (hashmap_it == hash_to_node_.end() || *node_it < *hashmap_it->second) {
      hash_to_node_[hash_val] = node_it;
    }
  }
}

void HashRing::RemoveNode(const IpAddr& node) {
  // This node must be in the set. Keep the iterator to erase it later.