/// <summary>
/// Checks whether the host <paramref name="h"/> should be skipped.
/// </summary>
private static bool ShouldSkipHost(NetworkTopologyTokenMapContext context, Host h, HashSet <string> racksPlacedInDc)
{
var replicaForRackAlreadySelected = h.Rack != null && racksPlacedInDc.Contains(h.Rack);
var racksMissing = racksPlacedInDc.Count < context.Datacenters[h.Datacenter].Racks.Count;
return(replicaForRackAlreadySelected && racksMissing);
}
/// <summary>
/// Get collection that contains the already added racks in the provided datacenter (<paramref name="dc"/>).
/// If there's no such collection for the specified datacenter, then create one.
/// </summary>
private static HashSet <string> GetAddedRacksInDatacenter(NetworkTopologyTokenMapContext context, string dc)
{
if (!context.RacksAdded.TryGetValue(dc, out var racksAddedInDc))
{
context.RacksAdded[dc] = racksAddedInDc = new HashSet <string>();
}
return(racksAddedInDc);
}
/// <summary>
/// This method doesn't guarantee that the host will be added to the skipped hosts collection.
/// It will depend on whether the collection already has enough hosts to satisfy the replication factor for the host's datacenter.
/// </summary>
private static void TryAddToSkippedHostsCollection(NetworkTopologyTokenMapContext context, Host h, int dcRf, int dcAddedReplicas)
{
// We already added a replica for this rack, skip until replicas in other racks are added
var remainingReplicasNeededToSatisfyRf = dcRf - dcAddedReplicas;
if (context.SkippedHosts.Count < remainingReplicasNeededToSatisfyRf)
{
// these replicas will be added in the end after a replica has been selected for every rack
context.SkippedHosts.Add(h);
}
}
/// <summary>
/// Add replicas that were skipped before to satisfy replication factor
/// </summary>
/// <returns>Number of replicas added to <see cref="NetworkTopologyTokenMapContext.TokenReplicas"/> of <paramref name="context"/></returns>
private static int AddSkippedHosts(NetworkTopologyTokenMapContext context, string dc, int dcRf, int dcReplicas)
{
var counter = 0;
var length = dcRf - dcReplicas;
foreach (var h in context.SkippedHosts.Where(h => h.Datacenter == dc))
{
context.TokenReplicas.Add(h);
if (++counter == length)
{
break;
}
}
return(counter);
}
private ISet <Host> ComputeReplicasForToken(
IReadOnlyList <IToken> ring,
IReadOnlyDictionary <IToken, Host> primaryReplicas,
IReadOnlyDictionary <string, DatacenterInfo> datacenters,
int i)
{
var context = new NetworkTopologyTokenMapContext(ring, primaryReplicas, datacenters);
for (var j = 0; j < ring.Count; j++)
{
// wrap around if necessary
var replicaIndex = (i + j) % ring.Count;
var replica = primaryReplicas[ring[replicaIndex]];
var dc = replica.Datacenter;
if (!_replicationFactorsMap.TryGetValue(dc, out var dcRfObj))
{
continue;
}
var dcRf = Math.Min(dcRfObj.FullReplicas, datacenters[dc].HostLength);
context.ReplicasByDc.TryGetValue(dc, out var dcAddedReplicas);
if (dcAddedReplicas >= dcRf)
{
// replication factor for the datacenter has already been satisfied
continue;
}
var racksAddedInDc = NetworkTopologyStrategy.GetAddedRacksInDatacenter(context, dc);
if (NetworkTopologyStrategy.ShouldSkipHost(context, replica, racksAddedInDc))
{
NetworkTopologyStrategy.TryAddToSkippedHostsCollection(context, replica, dcRf, dcAddedReplicas);
continue;
}
NetworkTopologyStrategy.AddReplica(context, replica, dcRf, dcAddedReplicas, racksAddedInDc);
if (NetworkTopologyStrategy.AreReplicationFactorsSatisfied(_replicationFactorsMap, context.ReplicasByDc, datacenters))
{
break;
}
}
return(context.TokenReplicas);
}
/// <summary>
/// Adds replica (<paramref name="host"/>) to <see cref="NetworkTopologyTokenMapContext.TokenReplicas"/> of <paramref name="context"/>
/// and adds skipped hosts if a replica has been added to every rack in datacenter the host's datacenter.
/// </summary>
private static void AddReplica(NetworkTopologyTokenMapContext context, Host host, int dcRf, int dcAddedReplicas, HashSet <string> racksPlacedInDc)
{
var dc = host.Datacenter;
if (context.TokenReplicas.Add(host))
{
dcAddedReplicas++;
}
context.ReplicasByDc[dc] = dcAddedReplicas;
var rackAdded = host.Rack != null && racksPlacedInDc.Add(host.Rack);
var allRacksPlacedInDc = racksPlacedInDc.Count == context.Datacenters[dc].Racks.Count;
if (rackAdded && allRacksPlacedInDc)
{
// We finished placing all replicas for all racks in this dc, add the skipped hosts
context.ReplicasByDc[dc] += NetworkTopologyStrategy.AddSkippedHosts(context, dc, dcRf, dcAddedReplicas);
}
}