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Rebalancer.java
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Rebalancer.java
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/*
* 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.server.rebalance;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.log4j.Logger;
import voldemort.VoldemortException;
import voldemort.client.protocol.admin.AdminClient;
import voldemort.client.rebalance.RebalancePartitionsInfo;
import voldemort.cluster.Cluster;
import voldemort.server.StoreRepository;
import voldemort.server.VoldemortConfig;
import voldemort.server.protocol.admin.AsyncOperationService;
import voldemort.server.rebalance.async.DonorBasedRebalanceAsyncOperation;
import voldemort.server.rebalance.async.StealerBasedRebalanceAsyncOperation;
import voldemort.store.StoreDefinition;
import voldemort.store.metadata.MetadataStore;
import voldemort.store.metadata.MetadataStore.VoldemortState;
import voldemort.store.readonly.ReadOnlyStorageConfiguration;
import voldemort.store.readonly.ReadOnlyStorageEngine;
import voldemort.utils.RebalanceUtils;
import voldemort.versioning.VectorClock;
import voldemort.versioning.Versioned;
import com.google.common.collect.Lists;
/**
* Service responsible for rebalancing
*
* <br>
*
* Handles two scenarios a) When a new request comes in b) When a rebalancing
* was shut down and the box was restarted
*
*/
public class Rebalancer implements Runnable {
private final static Logger logger = Logger.getLogger(Rebalancer.class);
private final MetadataStore metadataStore;
private final AsyncOperationService asyncService;
private final VoldemortConfig voldemortConfig;
private final StoreRepository storeRepository;
private final Set<Integer> rebalancePermits = Collections.synchronizedSet(new HashSet<Integer>());
public Rebalancer(StoreRepository storeRepository,
MetadataStore metadataStore,
VoldemortConfig voldemortConfig,
AsyncOperationService asyncService) {
this.storeRepository = storeRepository;
this.metadataStore = metadataStore;
this.asyncService = asyncService;
this.voldemortConfig = voldemortConfig;
}
public AsyncOperationService getAsyncOperationService() {
return asyncService;
}
public void start() {}
public void stop() {}
/**
* This is called only once at startup
*/
public void run() {}
/**
* Acquire a permit for a particular node id so as to allow rebalancing
*
* @param nodeId The id of the node for which we are acquiring a permit
* @return Returns true if permit acquired, false if the permit is already
* held by someone
*/
public synchronized boolean acquireRebalancingPermit(int nodeId) {
boolean added = rebalancePermits.add(nodeId);
logger.info("Acquiring rebalancing permit for node id " + nodeId + ", returned: " + added);
return added;
}
/**
* Release the rebalancing permit for a particular node id
*
* @param nodeId The node id whose permit we want to release
*/
public synchronized void releaseRebalancingPermit(int nodeId) {
boolean removed = rebalancePermits.remove(nodeId);
logger.info("Releasing rebalancing permit for node id " + nodeId + ", returned: " + removed);
if(!removed)
throw new VoldemortException(new IllegalStateException("Invalid state, must hold a "
+ "permit to release"));
}
/**
* Support four different stages <br>
* For normal operation:
*
* <pre>
* | swapRO | changeClusterMetadata | changeRebalanceState | Order |
* | f | t | t | cluster -> rebalance |
* | f | f | t | rebalance |
* | t | t | f | cluster -> swap |
* | t | t | t | cluster -> swap -> rebalance |
* </pre>
*
* In general we need to do [ cluster change -> swap -> rebalance state
* change ]
*
* NOTE: The update of the cluster metadata and the rebalancer state is not
* "atomic". Ergo, there could theoretically be a race where a client picks
* up new cluster metadata sends a request based on that, but the proxy
* bridges have not been setup and we either miss a proxy put or return a
* null for get/getalls
*
* @param cluster Cluster metadata to change
* @param rebalancePartitionsInfo List of rebalance partitions info
* @param swapRO Boolean to indicate swapping of RO store
* @param changeClusterMetadata Boolean to indicate a change of cluster
* metadata
* @param changeRebalanceState Boolean to indicate a change in rebalance
* state
* @param rollback Boolean to indicate that we are rolling back or not
*/
public void rebalanceStateChange(Cluster cluster,
List<RebalancePartitionsInfo> rebalancePartitionsInfo,
boolean swapRO,
boolean changeClusterMetadata,
boolean changeRebalanceState,
boolean rollback) {
Cluster currentCluster = metadataStore.getCluster();
logger.info("Server doing rebalance state change with options [ cluster metadata change - "
+ changeClusterMetadata + " ], [ changing rebalancing state - "
+ changeRebalanceState + " ], [ changing swapping RO - " + swapRO
+ " ], [ rollback - " + rollback + " ]");
// Variables to track what has completed
List<RebalancePartitionsInfo> completedRebalancePartitionsInfo = Lists.newArrayList();
List<String> swappedStoreNames = Lists.newArrayList();
boolean completedClusterChange = false;
boolean completedRebalanceSourceClusterChange = false;
Cluster previousRebalancingSourceCluster = null;
try {
// CHANGE CLUSTER METADATA
if(changeClusterMetadata) {
logger.info("Switching metadata from " + currentCluster + " to " + cluster);
changeCluster(MetadataStore.CLUSTER_KEY, cluster);
completedClusterChange = true;
}
// SWAP RO DATA FOR ALL STORES
if(swapRO) {
swapROStores(swappedStoreNames, false);
}
// CHANGE REBALANCING STATE
if(changeRebalanceState) {
try {
previousRebalancingSourceCluster = metadataStore.getRebalancingSourceCluster();
if(!rollback) {
// Save up the current cluster for Redirecting store
changeCluster(MetadataStore.REBALANCING_SOURCE_CLUSTER_XML, currentCluster);
completedRebalanceSourceClusterChange = true;
for(RebalancePartitionsInfo info: rebalancePartitionsInfo) {
metadataStore.addRebalancingState(info);
completedRebalancePartitionsInfo.add(info);
}
} else {
// Reset the rebalancing source cluster back to null
changeCluster(MetadataStore.REBALANCING_SOURCE_CLUSTER_XML, null);
completedRebalanceSourceClusterChange = true;
for(RebalancePartitionsInfo info: rebalancePartitionsInfo) {
metadataStore.deleteRebalancingState(info);
completedRebalancePartitionsInfo.add(info);
}
}
} catch(Exception e) {
throw new VoldemortException(e);
}
}
} catch(VoldemortException e) {
logger.error("Got exception while changing state, now rolling back changes", e);
// ROLLBACK CLUSTER CHANGE
if(completedClusterChange) {
try {
logger.info("Rolling back cluster.xml to " + currentCluster);
changeCluster(MetadataStore.CLUSTER_KEY, currentCluster);
} catch(Exception exception) {
logger.error("Error while rolling back cluster metadata to " + currentCluster,
exception);
}
}
// SWAP RO DATA FOR ALL COMPLETED STORES
if(swappedStoreNames.size() > 0) {
try {
swapROStores(swappedStoreNames, true);
} catch(Exception exception) {
logger.error("Error while swapping back to old state ", exception);
}
}
// CHANGE BACK ALL REBALANCING STATES FOR COMPLETED ONES
if(completedRebalancePartitionsInfo.size() > 0) {
if(!rollback) {
for(RebalancePartitionsInfo info: completedRebalancePartitionsInfo) {
try {
metadataStore.deleteRebalancingState(info);
} catch(Exception exception) {
logger.error("Error while deleting back rebalance info during error rollback "
+ info,
exception);
}
}
} else {
for(RebalancePartitionsInfo info: completedRebalancePartitionsInfo) {
try {
metadataStore.addRebalancingState(info);
} catch(Exception exception) {
logger.error("Error while adding back rebalance info during error rollback "
+ info,
exception);
}
}
}
}
// Revert changes to REBALANCING_SOURCE_CLUSTER_XML
if(completedRebalanceSourceClusterChange) {
logger.info("Reverting the REBALANCING_SOURCE_CLUSTER_XML back to "
+ previousRebalancingSourceCluster);
changeCluster(MetadataStore.REBALANCING_SOURCE_CLUSTER_XML,
previousRebalancingSourceCluster);
}
throw e;
}
}
/**
* Goes through all the RO Stores in the plan and swaps it
*
* @param swappedStoreNames Names of stores already swapped
* @param useSwappedStoreNames Swap only the previously swapped stores (
* Happens during error )
*/
private void swapROStores(List<String> swappedStoreNames, boolean useSwappedStoreNames) {
try {
for(StoreDefinition storeDef: metadataStore.getStoreDefList()) {
// Only pick up the RO stores
if(storeDef.getType().compareTo(ReadOnlyStorageConfiguration.TYPE_NAME) == 0) {
if(useSwappedStoreNames && !swappedStoreNames.contains(storeDef.getName())) {
continue;
}
ReadOnlyStorageEngine engine = (ReadOnlyStorageEngine) storeRepository.getStorageEngine(storeDef.getName());
if(engine == null) {
throw new VoldemortException("Could not find storage engine for "
+ storeDef.getName() + " to swap ");
}
logger.info("Swapping RO store " + storeDef.getName());
// Time to swap this store - Could have used admin client,
// but why incur the overhead?
engine.swapFiles(engine.getCurrentDirPath());
// Add to list of stores already swapped
if(!useSwappedStoreNames)
swappedStoreNames.add(storeDef.getName());
}
}
} catch(Exception e) {
logger.error("Error while swapping RO store");
throw new VoldemortException(e);
}
}
/**
* Updates the cluster metadata
*
* @param cluster The cluster metadata information
*/
private void changeCluster(String clusterKey, final Cluster cluster) {
try {
metadataStore.writeLock.lock();
try {
// TODO why increment server 0 all the time?
VectorClock updatedVectorClock = ((VectorClock) metadataStore.get(clusterKey, null)
.get(0)
.getVersion()).incremented(0,
System.currentTimeMillis());
metadataStore.put(clusterKey, Versioned.value((Object) cluster, updatedVectorClock));
} finally {
metadataStore.writeLock.unlock();
}
} catch(Exception e) {
logger.info("Error while changing cluster to " + cluster + "for key " + clusterKey);
throw new VoldemortException(e);
}
}
/**
* This function is responsible for starting the actual async rebalance
* operation. This is run if this node is the donor node
*
* <br>
*
* @param stealInfos List of partition infos to steal
* @return Returns a id identifying the async operation
*/
public int rebalanceNodeOnDonor(final List<RebalancePartitionsInfo> stealInfos) {
AdminClient adminClient = null;
List<Integer> stealerNodeIdsPermitsAcquired = Lists.newArrayList();
try {
adminClient = RebalanceUtils.createTempAdminClient(voldemortConfig,
metadataStore.getCluster(),
1);
int donorNodeId = metadataStore.getNodeId();
for(RebalancePartitionsInfo info: stealInfos) {
int stealerNodeId = info.getStealerId();
// Check if stealer node is in rebalancing state
if(!adminClient.rebalanceOps.getRemoteServerState(stealerNodeId)
.getValue()
.equals(VoldemortState.REBALANCING_MASTER_SERVER)) {
throw new VoldemortException("Stealer node " + stealerNodeId + " not in "
+ VoldemortState.REBALANCING_MASTER_SERVER
+ " state ");
}
// Also check if it has this plan
if(adminClient.rebalanceOps.getRemoteRebalancerState(stealerNodeId)
.getValue()
.find(donorNodeId) == null) {
throw new VoldemortException("Stealer node " + stealerNodeId
+ " does not have any plan for donor "
+ donorNodeId + ". Excepted to have " + info);
}
// Get a lock for the stealer node
if(!acquireRebalancingPermit(stealerNodeId)) {
throw new VoldemortException("Node " + metadataStore.getNodeId()
+ " is already trying to push to stealer node "
+ stealerNodeId);
}
// Add to list of permits acquired
stealerNodeIdsPermitsAcquired.add(stealerNodeId);
}
} catch(VoldemortException e) {
// Rollback acquired permits for some of the donor nodes
for(int stealerNodeId: stealerNodeIdsPermitsAcquired) {
releaseRebalancingPermit(stealerNodeId);
}
throw e;
} finally {
if(adminClient != null) {
adminClient.close();
}
}
// Acquired lock successfully, start rebalancing...
int requestId = asyncService.getUniqueRequestId();
// Why do we pass 'info' instead of 'stealInfo'? So that we can change
// the state as the stores finish rebalance
asyncService.submitOperation(requestId,
new DonorBasedRebalanceAsyncOperation(this,
storeRepository,
voldemortConfig,
metadataStore,
requestId,
stealInfos,
voldemortConfig.usePartitionScanForRebalance()));
return requestId;
}
/**
* This function is responsible for starting the actual async rebalance
* operation. This is run if this node is the stealer node
*
* <br>
*
* We also assume that the check that this server is in rebalancing state
* has been done at a higher level
*
* @param stealInfo Partition info to steal
* @return Returns a id identifying the async operation
*/
public int rebalanceNode(final RebalancePartitionsInfo stealInfo) {
final RebalancePartitionsInfo info = metadataStore.getRebalancerState()
.find(stealInfo.getDonorId());
// Do we have the plan in the state?
if(info == null) {
throw new VoldemortException("Could not find plan " + stealInfo
+ " in the server state on " + metadataStore.getNodeId());
} else if(!info.equals(stealInfo)) {
// If we do have the plan, is it the same
throw new VoldemortException("The plan in server state " + info
+ " is not the same as the process passed " + stealInfo);
} else if(!acquireRebalancingPermit(stealInfo.getDonorId())) {
// Both are same, now try to acquire a lock for the donor node
throw new AlreadyRebalancingException("Node " + metadataStore.getNodeId()
+ " is already rebalancing from donor "
+ info.getDonorId() + " with info " + info);
}
// Acquired lock successfully, start rebalancing...
int requestId = asyncService.getUniqueRequestId();
// Why do we pass 'info' instead of 'stealInfo'? So that we can change
// the state as the stores finish rebalance
asyncService.submitOperation(requestId,
new StealerBasedRebalanceAsyncOperation(this,
voldemortConfig,
metadataStore,
requestId,
info));
return requestId;
}
}