Interface ConsistentHash

All Known Implementing Classes:
AbstractConsistentHash, DefaultConsistentHash, ReplicatedConsistentHash
public interface ConsistentHash
A consistent hash algorithm implementation. Implementations would typically be constructed via a ConsistentHashFactory. A consistent hash assigns each key a list of owners; the number of owners is defined at creation time, but the consistent hash is free to return a smaller or a larger number of owners, depending on circumstances. The first element in the list of owners is the "primary owner". The other owners are called "backup owners". Some implementations guarantee that there will always be a primary owner, others do not. This interface gives access to some implementation details of the consistent hash. Our consistent hashes work by splitting the hash space (the set of possible hash codes) into fixed segments and then assigning those segments to nodes dynamically. The number of segments is defined at creation time, and the mapping of keys to segments never changes. The mapping of segments to nodes can change as the membership of the cache changes. Normally application code doesn't need to know about this implementation detail, but some applications may benefit from the knowledge that all the keys that map to one segment are always located on the same server.
Since:
4.0
Author:
Manik Surtani, Mircea.Markus@jboss.com, Dan Berindei, anistor@redhat.com
See Also:

  • Method Details

    • getNumSegments

      int getNumSegments()
      Returns:
      The actual number of hash space segments. Note that it may not be the same as the number of segments passed in at creation time.

    • getMembers

      List<Address> getMembers()
      Should return the addresses of the nodes used to create this consistent hash.
      Returns:
      list of node addresses.

    • locateOwnersForSegment

      List<Address> locateOwnersForSegment(int segmentId)
      Returns:
      All the nodes that own a given hash space segment, first address is the primary owner. The returned list is unmodifiable.

    • locatePrimaryOwnerForSegment

      Address locatePrimaryOwnerForSegment(int segmentId)
      Returns:
      The primary owner of a given hash space segment. This is equivalent to locateOwnersForSegment(segmentId).get(0) but is more efficient

    • isSegmentLocalToNode

      default boolean isSegmentLocalToNode(Address nodeAddress, int segmentId)
      Check if a segment is local to a given member.

      Implementation note: normally key-based method are implemented based on segment-based methods. Here, however, we need a default implementation for the segment-based method for backwards-compatibility reasons.

      Since:
      8.2

    • isReplicated

      default boolean isReplicated()
      Returns:
      true if every member owns every segment. This allows callers to skip computing the segment of a key in some cases.

    • getSegmentsForOwner

      Set<Integer> getSegmentsForOwner(Address owner)
      Returns the segments owned by a cache member.
      Parameters:
      owner - the address of the member
      Returns:
      a non-null set of segment IDs, may or may not be unmodifiable, which shouldn't be modified by caller. The set is empty if owner is not a member of the consistent hash.

    • getPrimarySegmentsForOwner

      Set<Integer> getPrimarySegmentsForOwner(Address owner)
      Returns the segments that this cache member is the primary owner for.
      Parameters:
      owner - the address of the member
      Returns:
      a non-null set of segment IDs, may or may not be unmodifiable, which shouldn't be modified by caller. The set is empty if owner is not a member of the consistent hash.

    • getRoutingTableAsString

      String getRoutingTableAsString()
      Returns a string containing all the segments and their associated addresses.

    • toScopedState

      default void toScopedState(ScopedPersistentState state, Function<Address,UUID> addressMapper)
      Writes this ConsistentHash to the specified scoped persistent state.
      Parameters:
      state - The state to which this ConsistentHash will be written.
      addressMapper - The mapper Function to convert the Address to the UUID used to persist the address within the state.

    • getCapacityFactors

      default Map<Address,Float> getCapacityFactors()
      The capacity factor of each member. Determines the relative capacity of each node compared to the others. If null, all the members are assumed to have a capacity factor of 1.