org.apache.cassandra.service
Class PendingRangeCalculatorService

java.lang.Object
  org.apache.cassandra.service.PendingRangeCalculatorServiceMBean
      org.apache.cassandra.service.PendingRangeCalculatorService

public class PendingRangeCalculatorService
extends PendingRangeCalculatorServiceMBean

Field Summary

static PendingRangeCalculatorService

instance

Constructor Summary

PendingRangeCalculatorService()

Method Summary

void	blockUntilFinished()
static void	calculatePendingRanges(AbstractReplicationStrategy strategy, java.lang.String table) Calculate pending ranges according to bootstrapping and leaving nodes.
java.util.concurrent.Future<?>	update()

Methods inherited from class java.lang.Object

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

Field Detail

instance

public static final PendingRangeCalculatorService instance

Constructor Detail

PendingRangeCalculatorService

public PendingRangeCalculatorService()

Method Detail

update

public java.util.concurrent.Future<?> update()

blockUntilFinished

public void blockUntilFinished()

calculatePendingRanges

public static void calculatePendingRanges(AbstractReplicationStrategy strategy,
                                          java.lang.String table)

Calculate pending ranges according to bootstrapping and leaving nodes. Reasoning is: (1) When in doubt, it is better to write too much to a node than too little. That is, if there are multiple nodes moving, calculate the biggest ranges a node could have. Cleaning up unneeded data afterwards is better than missing writes during movement. (2) When a node leaves, ranges for other nodes can only grow (a node might get additional ranges, but it will not lose any of its current ranges as a result of a leave). Therefore we will first remove _all_ leaving tokens for the sake of calculation and then check what ranges would go where if all nodes are to leave. This way we get the biggest possible ranges with regard current leave operations, covering all subsets of possible final range values. (3) When a node bootstraps, ranges of other nodes can only get smaller. Without doing complex calculations to see if multiple bootstraps overlap, we simply base calculations on the same token ring used before (reflecting situation after all leave operations have completed). Bootstrapping nodes will be added and removed one by one to that metadata and checked what their ranges would be. This will give us the biggest possible ranges the node could have. It might be that other bootstraps make our actual final ranges smaller, but it does not matter as we can clean up the data afterwards. NOTE: This is heavy and ineffective operation. This will be done only once when a node changes state in the cluster, so it should be manageable.