RebalanceController.java

/*
 * Copyright 2008-2013 LinkedIn, Inc
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package voldemort.client.rebalance;

import java.text.DecimalFormat;
import java.util.HashMap;
import java.util.List;
import java.util.Map.Entry;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

import org.apache.log4j.Logger;

import voldemort.VoldemortException;
import voldemort.client.ClientConfig;
import voldemort.client.protocol.admin.AdminClient;
import voldemort.client.protocol.admin.AdminClientConfig;
import voldemort.client.rebalance.task.DonorBasedRebalanceTask;
import voldemort.client.rebalance.task.RebalanceTask;
import voldemort.client.rebalance.task.StealerBasedRebalanceTask;
import voldemort.cluster.Cluster;
import voldemort.cluster.Node;
import voldemort.server.rebalance.VoldemortRebalancingException;
import voldemort.store.StoreDefinition;
import voldemort.utils.NodeUtils;
import voldemort.utils.Pair;
import voldemort.utils.RebalanceUtils;
import voldemort.utils.StoreDefinitionUtils;
import voldemort.utils.Utils;
import voldemort.versioning.Versioned;

import com.google.common.collect.Lists;

/**
 * Executes a RebalancePlan.
 * 
 */
public class RebalanceController {

    // TODO: Remove server side "optimization" that does not bother to steal
    // partition-stores it already hosts. That code will be unnecessary. This
    // also affects AdminClient that has an override of this option. Do not
    // complete this work until the atomic metadata update is merged with this
    // branch. Otherwise, there will be conflicts on .proto changes.

    private static final Logger logger = Logger.getLogger(RebalanceController.class);

    private static final DecimalFormat decimalFormatter = new DecimalFormat("#.##");

    private final AdminClient adminClient;
    private final Cluster currentCluster;
    private final List<StoreDefinition> currentStoreDefs;

    public final static int MAX_PARALLEL_REBALANCING = 1;
    public final static int MAX_TRIES_REBALANCING = 2;
    public final static boolean STEALER_BASED_REBALANCING = true;
    public final static long PROXY_PAUSE_IN_SECONDS = TimeUnit.MINUTES.toSeconds(5);

    private final int maxParallelRebalancing;
    private final int maxTriesRebalancing;
    private final boolean stealerBasedRebalancing;
    private final long proxyPauseS;

    public RebalanceController(String bootstrapUrl,
                               int maxParallelRebalancing,
                               int maxTriesRebalancing,
                               boolean stealerBased,
                               long proxyPauseS) {
        this.adminClient = new AdminClient(bootstrapUrl,
                                           new AdminClientConfig(),
                                           new ClientConfig());
        Pair<Cluster, List<StoreDefinition>> pair = getCurrentClusterState();
        this.currentCluster = pair.getFirst();
        this.currentStoreDefs = pair.getSecond();

        this.maxParallelRebalancing = maxParallelRebalancing;
        this.maxTriesRebalancing = maxTriesRebalancing;
        this.stealerBasedRebalancing = stealerBased;
        this.proxyPauseS = proxyPauseS;
    }

    /**
     * Probe the existing cluster to retrieve the current cluster xml and stores
     * xml.
     * 
     * @return Pair of Cluster and List<StoreDefinition> from current cluster.
     */
    private Pair<Cluster, List<StoreDefinition>> getCurrentClusterState() {

        // Retrieve the latest cluster metadata from the existing nodes
        Versioned<Cluster> currentVersionedCluster = RebalanceUtils.getLatestCluster(NodeUtils.getNodeIds(Lists.newArrayList(adminClient.getAdminClientCluster()
                                                                                                                                        .getNodes())),
                                                                                     adminClient);
        Cluster cluster = currentVersionedCluster.getValue();
        List<StoreDefinition> storeDefs = RebalanceUtils.getCurrentStoreDefinitions(cluster,
                                                                                    adminClient);
        return new Pair<Cluster, List<StoreDefinition>>(cluster, storeDefs);
    }

    /**
     * Construct a plan for the specified final cluster/stores & batchSize given
     * the current cluster/stores & configuration of the RebalanceController.
     * 
     * @param finalCluster
     * @param finalStoreDefs Needed for zone expansion/shrinking.
     * @param batchSize
     * @return
     */
    public RebalancePlan getPlan(Cluster finalCluster,
                                 List<StoreDefinition> finalStoreDefs,
                                 int batchSize) {
        RebalanceUtils.validateClusterStores(finalCluster, finalStoreDefs);
        // If an interim cluster is needed, then currentCluster should be an
        // interim cluster! I.e., it should include new nodes/zones without any
        // partitions assigned to them.
        RebalanceUtils.validateInterimFinalCluster(currentCluster, finalCluster);

        String outputDir = null;
        return new RebalancePlan(currentCluster,
                                 currentStoreDefs,
                                 finalCluster,
                                 finalStoreDefs,
                                 batchSize,
                                 outputDir);
    }

    /**
     * Construct a plan for the specified final cluster & batchSize given the
     * current cluster/stores & configuration of the RebalanceController.
     * 
     * @param finalCluster
     * @param batchSize
     * @return
     */
    public RebalancePlan getPlan(Cluster finalCluster, int batchSize) {
        return getPlan(finalCluster, currentStoreDefs, batchSize);
    }

    /**
     * Validate the plan, validate the cluster, and then kick off rebalance.
     * 
     * @param rebalancePlan
     */
    public void rebalance(final RebalancePlan rebalancePlan) {
        validateRebalancePlanState(rebalancePlan);
        validateClusterForRebalance(rebalancePlan);
        executePlan(rebalancePlan);
    }

    /**
     * Validates all aspects of the plan (i.e., all config files)
     * 
     * @param rebalancePlan
     */
    private void validateRebalancePlanState(RebalancePlan rebalancePlan) {
        logger.info("Validating rebalance plan state.");

        Cluster currentCluster = rebalancePlan.getCurrentCluster();
        List<StoreDefinition> currentStores = rebalancePlan.getCurrentStores();
        Cluster finalCluster = rebalancePlan.getFinalCluster();
        List<StoreDefinition> finalStores = rebalancePlan.getFinalStores();

        RebalanceUtils.validateClusterStores(currentCluster, currentStores);
        RebalanceUtils.validateClusterStores(finalCluster, finalStores);
        RebalanceUtils.validateCurrentFinalCluster(currentCluster, finalCluster);
        RebalanceUtils.validateRebalanceStore(currentStores);
        RebalanceUtils.validateRebalanceStore(finalStores);
    }

    /**
     * Validates deployed cluster:
     * <ul>
     * <li>sets local admin client to finalCluster
     * <li>checks that all servers are currently in normal state
     * <li>confirms read-only stores can be rebalanced.
     * </ul>
     * 
     * @param finalCluster
     * @param finalStores
     */
    private void validateClusterForRebalance(RebalancePlan rebalancePlan) {
        logger.info("Validating state of deployed cluster to confirm its ready for rebalance.");
        Cluster finalCluster = rebalancePlan.getFinalCluster();
        List<StoreDefinition> finalStoreDefs = rebalancePlan.getFinalStores();

        // Reset the cluster that the admin client points at
        adminClient.setAdminClientCluster(finalCluster);
        // Validate that all the nodes ( new + old ) are in normal state
        RebalanceUtils.checkEachServerInNormalState(finalCluster, adminClient);
        // Verify all old RO stores exist at version 2
        RebalanceUtils.validateReadOnlyStores(finalCluster, finalStoreDefs, adminClient);
    }

    /**
     * Executes the rebalance plan. Does so batch-by-batch. Between each batch,
     * status is dumped to logger.info.
     * 
     * @param rebalancePlan
     */
    private void executePlan(RebalancePlan rebalancePlan) {
        logger.info("Starting to execute rebalance Plan!");

        int batchCount = 0;
        int partitionStoreCount = 0;
        long totalTimeMs = 0;

        List<RebalanceBatchPlan> entirePlan = rebalancePlan.getPlan();
        int numBatches = entirePlan.size();
        int numPartitionStores = rebalancePlan.getPartitionStoresMoved();

        for(RebalanceBatchPlan batchPlan: entirePlan) {
            logger.info("========  REBALANCING BATCH " + (batchCount + 1) + "  ========");
            RebalanceUtils.printBatchLog(batchCount, logger, batchPlan.toString());

            long startTimeMs = System.currentTimeMillis();
            // ACTUALLY DO A BATCH OF REBALANCING!
            executeBatch(batchCount, batchPlan);
            totalTimeMs += (System.currentTimeMillis() - startTimeMs);

            // Bump up the statistics
            batchCount++;
            partitionStoreCount += batchPlan.getPartitionStoreMoves();
            batchStatusLog(batchCount,
                           numBatches,
                           partitionStoreCount,
                           numPartitionStores,
                           totalTimeMs);
        }
    }

    /**
     * Pretty print a progress update after each batch complete.
     * 
     * @param batchCount current batch
     * @param numBatches total number of batches
     * @param partitionStoreCount partition stores migrated
     * @param numPartitionStores total number of partition stores to migrate
     * @param totalTimeMs total time, in milliseconds, of execution thus far.
     */
    private void batchStatusLog(int batchCount,
                                int numBatches,
                                int partitionStoreCount,
                                int numPartitionStores,
                                long totalTimeMs) {
        // Calculate the estimated end time and pretty print stats
        double rate = 1;
        long estimatedTimeMs = 0;
        if(numPartitionStores > 0) {
            rate = partitionStoreCount / numPartitionStores;
            estimatedTimeMs = (long) (totalTimeMs / rate) - totalTimeMs;
        }

        StringBuilder sb = new StringBuilder();
        sb.append("Batch Complete!")
          .append(Utils.NEWLINE)
          .append("\tbatches moved: ")
          .append(batchCount)
          .append(" out of ")
          .append(numBatches)
          .append(Utils.NEWLINE)
          .append("\tPartition stores moved: ")
          .append(partitionStoreCount)
          .append(" out of ")
          .append(numPartitionStores)
          .append(Utils.NEWLINE)
          .append("\tPercent done: ")
          .append(decimalFormatter.format(rate * 100.0))
          .append(Utils.NEWLINE)
          .append("\tEstimated time left: ")
          .append(estimatedTimeMs)
          .append(" ms (")
          .append(TimeUnit.MILLISECONDS.toHours(estimatedTimeMs))
          .append(" hours)");
        RebalanceUtils.printBatchLog(batchCount, logger, sb.toString());
    }

    /**
     * Executes a batch plan.
     * 
     * @param batchId Used as the ID of the batch plan. This allows related
     *        tasks on client- & server-side to pretty print messages in a
     *        manner that debugging can track specific batch plans across the
     *        cluster.
     * @param batchPlan The batch plan...
     */
    private void executeBatch(int batchId, final RebalanceBatchPlan batchPlan) {
        final Cluster batchCurrentCluster = batchPlan.getCurrentCluster();
        final List<StoreDefinition> batchCurrentStoreDefs = batchPlan.getCurrentStoreDefs();
        final Cluster batchFinalCluster = batchPlan.getFinalCluster();
        final List<StoreDefinition> batchFinalStoreDefs = batchPlan.getFinalStoreDefs();

        try {
            final List<RebalancePartitionsInfo> rebalancePartitionsInfoList = batchPlan.getBatchPlan();

            if(rebalancePartitionsInfoList.isEmpty()) {
                RebalanceUtils.printBatchLog(batchId, logger, "Skipping batch " + batchId
                                                              + " since it is empty.");
                // Even though there is no rebalancing work to do, cluster
                // metadata must be updated so that the server is aware of the
                // new cluster xml.
                adminClient.rebalanceOps.rebalanceStateChange(batchCurrentCluster,
                                                              batchFinalCluster,
                                                              batchCurrentStoreDefs,
                                                              batchFinalStoreDefs,
                                                              rebalancePartitionsInfoList,
                                                              false,
                                                              true,
                                                              false,
                                                              false,
                                                              true);
                return;
            }

            RebalanceUtils.printBatchLog(batchId, logger, "Starting batch " + batchId + ".");

            // Split the store definitions
            List<StoreDefinition> readOnlyStoreDefs = StoreDefinitionUtils.filterStores(batchFinalStoreDefs,
                                                                                        true);
            List<StoreDefinition> readWriteStoreDefs = StoreDefinitionUtils.filterStores(batchFinalStoreDefs,
                                                                                         false);
            boolean hasReadOnlyStores = readOnlyStoreDefs != null && readOnlyStoreDefs.size() > 0;
            boolean hasReadWriteStores = readWriteStoreDefs != null
                                         && readWriteStoreDefs.size() > 0;

            // STEP 1 - Cluster state change
            boolean finishedReadOnlyPhase = false;
            List<RebalancePartitionsInfo> filteredRebalancePartitionPlanList = RebalanceUtils.filterPartitionPlanWithStores(rebalancePartitionsInfoList,
                                                                                                                            readOnlyStoreDefs);

            rebalanceStateChange(batchId,
                                 batchCurrentCluster,
                                 batchCurrentStoreDefs,
                                 batchFinalCluster,
                                 batchFinalStoreDefs,
                                 filteredRebalancePartitionPlanList,
                                 hasReadOnlyStores,
                                 hasReadWriteStores,
                                 finishedReadOnlyPhase);

            // STEP 2 - Move RO data
            if(hasReadOnlyStores) {
                proxyPause();
                RebalanceBatchPlanProgressBar progressBar = batchPlan.getProgressBar(batchId);
                executeSubBatch(batchId,
                                progressBar,
                                batchCurrentCluster,
                                batchCurrentStoreDefs,
                                filteredRebalancePartitionPlanList,
                                hasReadOnlyStores,
                                hasReadWriteStores,
                                finishedReadOnlyPhase);
            }

            // STEP 3 - Cluster change state
            finishedReadOnlyPhase = true;
            filteredRebalancePartitionPlanList = RebalanceUtils.filterPartitionPlanWithStores(rebalancePartitionsInfoList,
                                                                                              readWriteStoreDefs);

            rebalanceStateChange(batchId,
                                 batchCurrentCluster,
                                 batchCurrentStoreDefs,
                                 batchFinalCluster,
                                 batchFinalStoreDefs,
                                 filteredRebalancePartitionPlanList,
                                 hasReadOnlyStores,
                                 hasReadWriteStores,
                                 finishedReadOnlyPhase);

            // STEP 4 - Move RW data
            if(hasReadWriteStores) {
                if(!hasReadOnlyStores) {
                    proxyPause();
                }
                RebalanceBatchPlanProgressBar progressBar = batchPlan.getProgressBar(batchId);
                executeSubBatch(batchId,
                                progressBar,
                                batchCurrentCluster,
                                batchCurrentStoreDefs,
                                filteredRebalancePartitionPlanList,
                                hasReadOnlyStores,
                                hasReadWriteStores,
                                finishedReadOnlyPhase);
            }

            RebalanceUtils.printBatchLog(batchId, logger, "Successfully terminated batch "
                                                          + batchId + ".");

        } catch(Exception e) {
            RebalanceUtils.printErrorLog(batchId,
                                         logger,
                                         "Error in batch " + batchId + " - " + e.getMessage(),
                                         e);
            throw new VoldemortException("Rebalance failed on batch " + batchId, e);
        }
    }

    /**
     * Pause between cluster change in metadata and starting server rebalancing
     * work.
     */
    private void proxyPause() {
        logger.info("Pausing after cluster state has changed to allow proxy bridges to be established. "
                    + "Will start rebalancing work on servers in " + proxyPauseS + " seconds.");
        try {
            Thread.sleep(TimeUnit.SECONDS.toMillis(proxyPauseS));
        } catch(InterruptedException e) {
            logger.warn("Sleep interrupted in proxy pause.");
        }
    }

    /**
     * 
     * Perform a group of state change actions. Also any errors + rollback
     * procedures are performed at this level itself.
     * 
     * <pre>
     * | Case | hasRO | hasRW | finishedRO | Action |
     * | 0 | t | t | t | 2nd one ( cluster change + swap + rebalance state change ) |
     * | 1 | t | t | f | 1st one ( rebalance state change ) |
     * | 2 | t | f | t | 2nd one ( cluster change + swap ) |
     * | 3 | t | f | f | 1st one ( rebalance state change ) |
     * | 4 | f | t | t | 2nd one ( cluster change + rebalance state change ) |
     * | 5 | f | t | f | ignore |
     * | 6 | f | f | t | no stores, exception | 
     * | 7 | f | f | f | no stores, exception |
     * </pre>
     * 
     * Truth table, FTW!
     * 
     * @param batchId Rebalancing task id
     * @param batchCurrentCluster Current cluster
     * @param batchFinalCluster Transition cluster to propagate
     * @param rebalancePartitionPlanList List of partition plan list
     * @param hasReadOnlyStores Boolean indicating if read-only stores exist
     * @param hasReadWriteStores Boolean indicating if read-write stores exist
     * @param finishedReadOnlyStores Boolean indicating if we have finished RO
     *        store migration
     */
    private void rebalanceStateChange(final int batchId,
                                      Cluster batchCurrentCluster,
                                      List<StoreDefinition> batchCurrentStoreDefs,
                                      Cluster batchFinalCluster,
                                      List<StoreDefinition> batchFinalStoreDefs,
                                      List<RebalancePartitionsInfo> rebalancePartitionPlanList,
                                      boolean hasReadOnlyStores,
                                      boolean hasReadWriteStores,
                                      boolean finishedReadOnlyStores) {
        try {
            if(!hasReadOnlyStores && !hasReadWriteStores) {
                // Case 6 / 7 - no stores, exception
                throw new VoldemortException("Cannot get this state since it means there are no stores");
            } else if(!hasReadOnlyStores && hasReadWriteStores && !finishedReadOnlyStores) {
                // Case 5 - ignore
                RebalanceUtils.printBatchLog(batchId,
                                             logger,
                                             "Ignoring state change since there are no read-only stores");
            } else if(!hasReadOnlyStores && hasReadWriteStores && finishedReadOnlyStores) {
                // Case 4 - cluster change + rebalance state change
                RebalanceUtils.printBatchLog(batchId,
                                             logger,
                                             "Cluster metadata change + rebalance state change");
                adminClient.rebalanceOps.rebalanceStateChange(batchCurrentCluster,
                                                              batchFinalCluster,
                                                              batchCurrentStoreDefs,
                                                              batchFinalStoreDefs,
                                                              rebalancePartitionPlanList,
                                                              false,
                                                              true,
                                                              true,
                                                              true,
                                                              true);
            } else if(hasReadOnlyStores && !finishedReadOnlyStores) {
                // Case 1 / 3 - rebalance state change
                RebalanceUtils.printBatchLog(batchId, logger, "Rebalance state change");
                adminClient.rebalanceOps.rebalanceStateChange(batchCurrentCluster,
                                                              batchFinalCluster,
                                                              batchCurrentStoreDefs,
                                                              batchFinalStoreDefs,
                                                              rebalancePartitionPlanList,
                                                              false,
                                                              false,
                                                              true,
                                                              true,
                                                              true);
            } else if(hasReadOnlyStores && !hasReadWriteStores && finishedReadOnlyStores) {
                // Case 2 - swap + cluster change
                RebalanceUtils.printBatchLog(batchId, logger, "Swap + Cluster metadata change");
                adminClient.rebalanceOps.rebalanceStateChange(batchCurrentCluster,
                                                              batchFinalCluster,
                                                              batchCurrentStoreDefs,
                                                              batchFinalStoreDefs,
                                                              rebalancePartitionPlanList,
                                                              true,
                                                              true,
                                                              false,
                                                              true,
                                                              true);
            } else {
                // Case 0 - swap + cluster change + rebalance state change
                RebalanceUtils.printBatchLog(batchId,
                                             logger,
                                             "Swap + Cluster metadata change + rebalance state change");
                adminClient.rebalanceOps.rebalanceStateChange(batchCurrentCluster,
                                                              batchFinalCluster,
                                                              batchCurrentStoreDefs,
                                                              batchFinalStoreDefs,
                                                              rebalancePartitionPlanList,
                                                              true,
                                                              true,
                                                              true,
                                                              true,
                                                              true);
            }

        } catch(VoldemortRebalancingException e) {
            RebalanceUtils.printErrorLog(batchId,
                                         logger,
                                         "Failure while changing rebalancing state",
                                         e);
            throw e;
        }
    }

    // TODO: (refactor) Break this state-machine like method into multiple "sub"
    // methods. AFAIK, this method either does the RO stores or the RW stores in
    // a batch. I.e., there are at most 2 sub-batches for any given batch. And,
    // in practice, there is one sub-batch that is either RO or RW.
    // TODO: Fix the javadoc comment to be more easily understood.
    /**
     * The smallest granularity of rebalancing where-in we move partitions for a
     * sub-set of stores. Finally at the end of the movement, the node is
     * removed out of rebalance state
     * 
     * <br>
     * 
     * Also any errors + rollback procedures are performed at this level itself.
     * 
     * <pre>
     * | Case | hasRO | hasRW | finishedRO | Action |
     * | 0 | t | t | t | rollback cluster change + swap |
     * | 1 | t | t | f | nothing to do since "rebalance state change" should have removed everything |
     * | 2 | t | f | t | won't be triggered since hasRW is false |
     * | 3 | t | f | f | nothing to do since "rebalance state change" should have removed everything |
     * | 4 | f | t | t | rollback cluster change |
     * | 5 | f | t | f | won't be triggered |
     * | 6 | f | f | t | won't be triggered | 
     * | 7 | f | f | f | won't be triggered |
     * </pre>
     * 
     * @param batchId Rebalance task id
     * @param batchRollbackCluster Cluster to rollback to if we have a problem
     * @param rebalancePartitionPlanList The list of rebalance partition plans
     * @param hasReadOnlyStores Are we rebalancing any read-only stores?
     * @param hasReadWriteStores Are we rebalancing any read-write stores?
     * @param finishedReadOnlyStores Have we finished rebalancing of read-only
     *        stores?
     */
    private void executeSubBatch(final int batchId,
                                 RebalanceBatchPlanProgressBar progressBar,
                                 final Cluster batchRollbackCluster,
                                 final List<StoreDefinition> batchRollbackStoreDefs,
                                 final List<RebalancePartitionsInfo> rebalancePartitionPlanList,
                                 boolean hasReadOnlyStores,
                                 boolean hasReadWriteStores,
                                 boolean finishedReadOnlyStores) {
        RebalanceUtils.printBatchLog(batchId, logger, "Submitting rebalance tasks ");

        // Get an ExecutorService in place used for submitting our tasks
        ExecutorService service = RebalanceUtils.createExecutors(maxParallelRebalancing);

        // Sub-list of the above list
        final List<RebalanceTask> failedTasks = Lists.newArrayList();
        final List<RebalanceTask> incompleteTasks = Lists.newArrayList();

        // Semaphores for donor nodes - To avoid multiple disk sweeps
        Semaphore[] donorPermits = new Semaphore[batchRollbackCluster.getNumberOfNodes()];
        for(Node node: batchRollbackCluster.getNodes()) {
            donorPermits[node.getId()] = new Semaphore(1);
        }

        try {
            // List of tasks which will run asynchronously
            List<RebalanceTask> allTasks = executeTasks(batchId,
                                                        progressBar,
                                                        service,
                                                        rebalancePartitionPlanList,
                                                        donorPermits);
            RebalanceUtils.printBatchLog(batchId, logger, "All rebalance tasks submitted");

            // Wait and shutdown after (infinite) timeout
            RebalanceUtils.executorShutDown(service, Long.MAX_VALUE);
            RebalanceUtils.printBatchLog(batchId, logger, "Finished waiting for executors");

            // Collects all failures + incomplete tasks from the rebalance
            // tasks.
            List<Exception> failures = Lists.newArrayList();
            for(RebalanceTask task: allTasks) {
                if(task.hasException()) {
                    failedTasks.add(task);
                    failures.add(task.getError());
                } else if(!task.isComplete()) {
                    incompleteTasks.add(task);
                }
            }

            if(failedTasks.size() > 0) {
                throw new VoldemortRebalancingException("Rebalance task terminated unsuccessfully on tasks "
                                                                + failedTasks,
                                                        failures);
            }

            // If there were no failures, then we could have had a genuine
            // timeout ( Rebalancing took longer than the operator expected ).
            // We should throw a VoldemortException and not a
            // VoldemortRebalancingException ( which will start reverting
            // metadata ). The operator may want to manually then resume the
            // process.
            if(incompleteTasks.size() > 0) {
                throw new VoldemortException("Rebalance tasks are still incomplete / running "
                                             + incompleteTasks);
            }

        } catch(VoldemortRebalancingException e) {

            logger.error("Failure while migrating partitions for rebalance task " + batchId);

            if(hasReadOnlyStores && hasReadWriteStores && finishedReadOnlyStores) {
                // Case 0
                adminClient.rebalanceOps.rebalanceStateChange(null,
                                                              batchRollbackCluster,
                                                              null,
                                                              batchRollbackStoreDefs,
                                                              null,
                                                              true,
                                                              true,
                                                              false,
                                                              false,
                                                              false);
            } else if(hasReadWriteStores && finishedReadOnlyStores) {
                // Case 4
                adminClient.rebalanceOps.rebalanceStateChange(null,
                                                              batchRollbackCluster,
                                                              null,
                                                              batchRollbackStoreDefs,
                                                              null,
                                                              false,
                                                              true,
                                                              false,
                                                              false,
                                                              false);
            }

            throw e;

        } finally {
            if(!service.isShutdown()) {
                RebalanceUtils.printErrorLog(batchId,
                                             logger,
                                             "Could not shutdown service cleanly for rebalance task "
                                                     + batchId,
                                             null);
                service.shutdownNow();
            }
        }
    }

    private List<RebalanceTask> executeTasks(final int batchId,
                                             RebalanceBatchPlanProgressBar progressBar,
                                             final ExecutorService service,
                                             List<RebalancePartitionsInfo> rebalancePartitionPlanList,
                                             Semaphore[] donorPermits) {
        List<RebalanceTask> taskList = Lists.newArrayList();
        int taskId = 0;
        if(stealerBasedRebalancing) {
            for(RebalancePartitionsInfo partitionsInfo: rebalancePartitionPlanList) {
                StealerBasedRebalanceTask rebalanceTask = new StealerBasedRebalanceTask(batchId,
                                                                                        taskId,
                                                                                        partitionsInfo,
                                                                                        maxTriesRebalancing,
                                                                                        donorPermits[partitionsInfo.getDonorId()],
                                                                                        adminClient,
                                                                                        progressBar);
                taskList.add(rebalanceTask);
                service.execute(rebalanceTask);
                taskId++;
            }
        } else {
            // Group by donor nodes
            HashMap<Integer, List<RebalancePartitionsInfo>> donorNodeBasedPartitionsInfo = RebalanceUtils.groupPartitionsInfoByNode(rebalancePartitionPlanList,
                                                                                                                                    false);
            for(Entry<Integer, List<RebalancePartitionsInfo>> entries: donorNodeBasedPartitionsInfo.entrySet()) {
                DonorBasedRebalanceTask rebalanceTask = new DonorBasedRebalanceTask(batchId,
                                                                                    taskId,
                                                                                    entries.getValue(),
                                                                                    donorPermits[entries.getValue()
                                                                                                        .get(0)
                                                                                                        .getDonorId()],
                                                                                    adminClient,
                                                                                    progressBar);
                taskList.add(rebalanceTask);
                service.execute(rebalanceTask);
                taskId++;
            }
        }
        return taskList;
    }

    public AdminClient getAdminClient() {
        return adminClient;
    }

    public Cluster getCurrentCluster() {
        return currentCluster;
    }

    public List<StoreDefinition> getCurrentStoreDefs() {
        return currentStoreDefs;
    }

    public void stop() {
        adminClient.close();
    }

}