Package org.apache.druid.server.coordinator.balancer

Class CostBalancerStrategy

java.lang.Object
org.apache.druid.server.coordinator.balancer.CostBalancerStrategy
All Implemented Interfaces:
BalancerStrategy
Direct Known Subclasses:
CachingCostBalancerStrategy, DiskNormalizedCostBalancerStrategy
public class CostBalancerStrategy extends Object implements BalancerStrategy

  • Constructor Details

    • CostBalancerStrategy

      public CostBalancerStrategy(com.google.common.util.concurrent.ListeningExecutorService exec)

  • Method Details

    • computeJointSegmentsCost

      public static double computeJointSegmentsCost(DataSegment segment, Iterable<DataSegment> segmentSet)

    • computeJointSegmentsCost

      public static double computeJointSegmentsCost(DataSegment segmentA, DataSegment segmentB)
      This defines the unnormalized cost function between two segments. See https://github.com/apache/druid/pull/2972 for more details about the cost function. intervalCost: segments close together are more likely to be queried together multiplier: if two segments belong to the same data source, they are more likely to be involved in the same queries
      Parameters:
      segmentA - The first DataSegment.
      segmentB - The second DataSegment.
      Returns:
      the joint cost of placing the two DataSegments together on one node.

    • intervalCost

      public static double intervalCost(org.joda.time.Interval intervalA, org.joda.time.Interval intervalB)

    • intervalCost

      public static double intervalCost(double x1, double y0, double y1)
      Computes the joint cost of two intervals X = [x_0 = 0, x_1) and Y = [y_0, y_1) cost(X, Y) = \int_{x_0}^{x_1} \int_{y_0}^{y_1} e^{-\lambda |x-y|}dxdy $$ lambda = 1 in this particular implementation Other values of lambda can be calculated by multiplying inputs by lambda and multiplying the result by 1 / lambda ^ 2 Interval start and end are all relative to x_0. Therefore this function assumes x_0 = 0, x1 >= 0, and y1 > y0
      Parameters:
      x1 - end of interval X
      y0 - start of interval Y
      y1 - end o interval Y
      Returns:
      joint cost of X and Y

    • findServersToLoadSegment

      public Iterator<ServerHolder> findServersToLoadSegment(DataSegment segmentToLoad, List<ServerHolder> serverHolders)
      Description copied from interface: BalancerStrategy
      Finds the best servers to load the given segment. This method can be used both for placing the first copy of a segment in a tier or a replica of an already available segment.
      Specified by:
      findServersToLoadSegment in interface BalancerStrategy
      Returns:
      Iterator over the best servers (in order of preference) to load the segment.

    • findDestinationServerToMoveSegment

      public ServerHolder findDestinationServerToMoveSegment(DataSegment segmentToMove, ServerHolder sourceServer, List<ServerHolder> serverHolders)
      Description copied from interface: BalancerStrategy
      Finds the best server from the list of destinationServers to load the segmentToMove, if it is moved from the sourceServer.

      In order to avoid unnecessary moves when the segment is already optimally placed, include the sourceServer in the list of destinationServers.

      Specified by:
      findDestinationServerToMoveSegment in interface BalancerStrategy
      Returns:
      The server to move to, or null if the segment is already optimally placed.

    • findServersToDropSegment

      public Iterator<ServerHolder> findServersToDropSegment(DataSegment segmentToDrop, List<ServerHolder> serverHolders)
      Description copied from interface: BalancerStrategy
      Finds the best servers to drop the given segment.
      Specified by:
      findServersToDropSegment in interface BalancerStrategy
      Returns:
      Iterator over the servers (in order of preference) to drop the segment

    • getStats

      public CoordinatorRunStats getStats()
      Description copied from interface: BalancerStrategy
      Returns the stats collected by the strategy.
      Specified by:
      getStats in interface BalancerStrategy

    • computePlacementCost

      protected double computePlacementCost(DataSegment proposalSegment, ServerHolder server)
      Computes the cost of placing a segment on this server.