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

Class SegmentToMoveCalculator

java.lang.Object

org.apache.druid.server.coordinator.balancer.SegmentToMoveCalculator

public class SegmentToMoveCalculator
extends Object

Calculates the maximum, minimum and required number of segments to move in a Coordinator run for balancing.

Method Summary

Modifier and Type	Method	Description
static int	computeMaxSegmentsToMovePerTier(int totalSegments, int numBalancerThreads, org.joda.time.Duration coordinatorPeriod)	Calculates the maximum number of segments that can be picked for moving in the cluster in a single coordinator run.
static int	computeMinSegmentsToMoveInTier(int totalSegmentsInTier)	Calculates the minimum number of segments that should be considered for moving in a tier, so that the cluster is always balancing itself.
static int	computeNumSegmentsToMoveInTier(String tier, List<ServerHolder> historicals, int maxSegmentsToMoveInTier)	Calculates the number of segments to be picked for moving in the given tier, based on the level of skew between the historicals in the tier.
static int	computeNumSegmentsToMoveToBalanceTier(String tier, List<ServerHolder> historicals)	Computes the number of segments that need to be moved across the historicals in a tier to attain balance in terms of disk usage and segment counts per data source.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

computeNumSegmentsToMoveInTier

public static int computeNumSegmentsToMoveInTier(String tier,
                                                 List<ServerHolder> historicals,
                                                 int maxSegmentsToMoveInTier)

Calculates the number of segments to be picked for moving in the given tier, based on the level of skew between the historicals in the tier.

Parameters:

tier - Name of tier used for logging purposes

historicals - Active historicals in tier

maxSegmentsToMoveInTier - Maximum number of segments allowed to be moved in the tier.

Returns:

Number of segments to move in the tier in the range [MIN_SEGMENTS_TO_MOVE, maxSegmentsToMoveInTier].

computeMinSegmentsToMoveInTier

public static int computeMinSegmentsToMoveInTier(int totalSegmentsInTier)

Calculates the minimum number of segments that should be considered for moving in a tier, so that the cluster is always balancing itself.

This value must be calculated separately for every tier.

Parameters:

totalSegmentsInTier - Total number of all replicas of all segments loaded or queued across all historicals in the tier.

Returns:

minSegmentsToMoveInTier in the range [MIN_SEGMENTS_TO_MOVE, ~0.15% of totalSegmentsInTier].

computeMaxSegmentsToMovePerTier

public static int computeMaxSegmentsToMovePerTier(int totalSegments,
                                                  int numBalancerThreads,
                                                  org.joda.time.Duration coordinatorPeriod)

Calculates the maximum number of segments that can be picked for moving in the cluster in a single coordinator run.

This value must be calculated at the cluster level and then applied to every tier so that the total computation time is estimated correctly.

Each balancer thread can perform 1 billion computations in 20s (see #14584). Therefore, keeping a buffer of 10s, in every 30s:

 numComputations = maxSegmentsToMove * totalSegments

 maxSegmentsToMove = numComputations / totalSegments
                   = (nThreads * 1B) / totalSegments
 

Parameters:

totalSegments - Total number of all replicas of all segments loaded or queued across all historicals in the cluster.

Returns:

maxSegmentsToMove per tier in the range [MIN_SEGMENTS_TO_MOVE, ~20% of totalSegments].

See Also:

#14584

computeNumSegmentsToMoveToBalanceTier

public static int computeNumSegmentsToMoveToBalanceTier(String tier,
                                                        List<ServerHolder> historicals)

Computes the number of segments that need to be moved across the historicals in a tier to attain balance in terms of disk usage and segment counts per data source.

Parameters:

tier - Name of the tier used only for logging purposes

historicals - List of historicals in the tier