com.datastax.driver.core.policies.LatencyAwarePolicy java code examples

loadBalancingPolicy = LatencyAwarePolicy.builder(loadBalancingPolicy).build();

double currentMin = latencyTracker.getMinAverage();
for (Map.Entry<Host, Snapshot.Stats> entry :
  getScoresSnapshot().getAllStats().entrySet()) {
 Host host = entry.getKey();
 Snapshot.Stats stats = entry.getValue();

 /**
  * Builds a new latency aware policy using the options set on this builder.
  *
  * @return the newly created {@code LatencyAwarePolicy}.
  */
 public LatencyAwarePolicy build() {
  return new LatencyAwarePolicy(
    childPolicy, exclusionThreshold, scale, retryPeriod, updateRate, minMeasure);
 }
}

primingClient.prime(queryBuilder().withQuery(query).build());
LatencyAwarePolicy latencyAwarePolicy =
  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).hasSize(1);
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

  queryBuilder().withQuery(query).withThen(then().withResult(unavailable)).build());
LatencyAwarePolicy latencyAwarePolicy =
  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).isEmpty();
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).hasSize(1);
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

Builder builder = LatencyAwarePolicy.builder((LoadBalancingPolicy) paramList.get(0));

for (Map.Entry<Host, Snapshot.Stats> entry : getScoresSnapshot().getAllStats().entrySet()) {
  Host host = entry.getKey();
  Snapshot.Stats stats = entry.getValue();

  /**
   * Builds a new latency aware policy using the options set on this
   * builder.
   *
   * @return the newly created {@code LatencyAwarePolicy}.
   */
  public LatencyAwarePolicy build() {
    return new LatencyAwarePolicy(childPolicy, exclusionThreshold, scale, retryPeriod, updateRate, minMeasure);
  }
}

primingClient.prime(queryBuilder().withQuery(query).build());
LatencyAwarePolicy latencyAwarePolicy =
  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).hasSize(1);
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

  public static LoadBalancingPolicy getLoadBalancingPolicy(String policy) {
    LoadBalancingPolicy loadBalancingPolicy;
    switch (policy) {
      case tokenAwarePolicy:
        loadBalancingPolicy = new TokenAwarePolicy(new RoundRobinPolicy());
        break;
      case tokenDcAwareRoundRobinPolicy:
        loadBalancingPolicy = new TokenAwarePolicy(DCAwareRoundRobinPolicy.builder().build());
        break;
      case tokenLatencyAwarePolicy:
        loadBalancingPolicy = new TokenAwarePolicy(LatencyAwarePolicy.builder(new RoundRobinPolicy()).build());
        break;
      default:
        throw new IllegalArgumentException("Cassandra load balancing policy can be " + tokenAwarePolicy + " ," + tokenLatencyAwarePolicy
            + " ," + tokenDcAwareRoundRobinPolicy);
    }
    return loadBalancingPolicy;
  }
}

for (Map.Entry<Host, Snapshot.Stats> entry : getScoresSnapshot().getAllStats().entrySet()) {
  Host host = entry.getKey();
  Snapshot.Stats stats = entry.getValue();

  /**
   * Builds a new latency aware policy using the options set on this
   * builder.
   *
   * @return the newly created {@code LatencyAwarePolicy}.
   */
  public LatencyAwarePolicy build() {
    return new LatencyAwarePolicy(childPolicy, exclusionThreshold, scale, retryPeriod, updateRate, minMeasure);
  }
}

  queryBuilder().withQuery(query).withThen(then().withResult(unavailable)).build());
LatencyAwarePolicy latencyAwarePolicy =
  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).isEmpty();
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

  public LoadBalancingPolicy getLoadBalancingPolicy(String policy) {
    LoadBalancingPolicy loadBalancingPolicy = new RoundRobinPolicy();
    switch (policy) {
    case roundRobinPolicy:
      loadBalancingPolicy = new RoundRobinPolicy();
      break;
    case tokenAwarePolicy:
      loadBalancingPolicy = new TokenAwarePolicy(new RoundRobinPolicy());
      break;
    case dcAwareRoundRobinPolicy:
      loadBalancingPolicy = DCAwareRoundRobinPolicy.builder().build();
      break;
    case latencyAwarePolicy:
      loadBalancingPolicy = LatencyAwarePolicy.builder(new RoundRobinPolicy()).build();
      break;
    case errorAwarePolicy:
      loadBalancingPolicy = ErrorAwarePolicy.builder(new RoundRobinPolicy()).build();
      break;
    default:
      throw new IllegalArgumentException("Cassandra load balancing policy can be " + roundRobinPolicy + " ," + tokenAwarePolicy 
          + " ," + dcAwareRoundRobinPolicy);
    }
    return loadBalancingPolicy;
  }
}

for (Map.Entry<Host, Snapshot.Stats> entry : getScoresSnapshot().getAllStats().entrySet()) {
  Host host = entry.getKey();
  Snapshot.Stats stats = entry.getValue();

  /**
   * Builds a new latency aware policy using the options set on this
   * builder.
   *
   * @return the newly created {@code LatencyAwarePolicy}.
   */
  public LatencyAwarePolicy build() {
    return new LatencyAwarePolicy(childPolicy, exclusionThreshold, scale, retryPeriod, updateRate, minMeasure);
  }
}

  LatencyAwarePolicy.builder(new RoundRobinPolicy()).withMininumMeasurements(1).build();
Cluster.Builder builder = super.createClusterBuilder();
builder.withLoadBalancingPolicy(latencyAwarePolicy);
 LatencyAwarePolicy.Snapshot snapshot = latencyAwarePolicy.getScoresSnapshot();
 assertThat(snapshot.getAllStats()).hasSize(1);
 LatencyAwarePolicy.Snapshot.Stats stats = snapshot.getStats(retrieveSingleHost(cluster));

if (loadBalancingProp != null) {
  if ("LatencyAwareRoundRobinPolicy".equals(loadBalancingProp)) {
    builder = builder.withLoadBalancingPolicy(LatencyAwarePolicy.builder(new RoundRobinPolicy()).build());
  } else if ("RoundRobinPolicy".equals(loadBalancingProp)) {
    builder = builder.withLoadBalancingPolicy(new RoundRobinPolicy());

for (Map.Entry<Host, Snapshot.Stats> entry : getScoresSnapshot().getAllStats().entrySet()) {
  Host host = entry.getKey();
  Snapshot.Stats stats = entry.getValue();

Javadoc

A wrapper load balancing policy that adds latency awareness to a child policy.

When used, this policy will collect the latencies of the queries to each Cassandra node and maintain a per-node latency score (an average). Based on these scores, the policy will penalize (technically, it will ignore them unless no other nodes are up) the nodes that are slower than the best performing node by more than some configurable amount (the exclusion threshold).

The latency score for a given node is a based on a form of exponential moving average. In other words, the latency score of a node is the average of its previously measured latencies, but where older measurements gets an exponentially decreasing weight. The exact weight applied to a newly received latency is based on the time elapsed since the previous measure (to account for the fact that latencies are not necessarily reported with equal regularity, neither over time nor between different nodes).

Once a node is excluded from query plans (because its averaged latency grew over the exclusion threshold), its latency score will not be updated anymore (since it is not queried). To give a chance to this node to recover, the policy has a configurable retry period. The policy will not penalize a host for which no measurement has been collected for more than this retry period.

Please see the Builder class and methods for more details on the possible parameters of this policy.

Most used methods

builder
Creates a new latency aware policy builder given the child policy that the resulting policy should w
getScoresSnapshot
Returns a snapshot of the scores (latency averages) maintained by this policy.
<init>

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How to useLatencyAwarePolicy in com.datastax.driver.core.policies

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