/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.hadoop.hbase.master.balancer;
import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseInterfaceAudience;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.NamespaceDescriptor;
import org.apache.hadoop.hbase.ServerLoad;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.master.LoadBalancer;
import org.apache.hadoop.hbase.master.RackManager;
import org.apache.hadoop.hbase.master.RegionPlan;
import org.apache.hadoop.hbase.master.ServerManager;
import org.apache.hadoop.hbase.master.SnapshotOfRegionAssignmentFromMeta;
import org.apache.hadoop.hbase.master.balancer.FavoredNodesPlan.Position;
import org.apache.hadoop.hbase.util.Pair;
/**
* An implementation of the {@link LoadBalancer} that assigns favored nodes for
* each region. There is a Primary RegionServer that hosts the region, and then
* there is Secondary and Tertiary RegionServers. Currently, the favored nodes
* information is used in creating HDFS files - the Primary RegionServer passes
* the primary, secondary, tertiary node addresses as hints to the DistributedFileSystem
* API for creating files on the filesystem. These nodes are treated as hints by
* the HDFS to place the blocks of the file. This alleviates the problem to do with
* reading from remote nodes (since we can make the Secondary RegionServer as the new
* Primary RegionServer) after a region is recovered. This should help provide consistent
* read latencies for the regions even when their primary region servers die.
*
*/
@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.CONFIG)
public class FavoredNodeLoadBalancer extends BaseLoadBalancer {
private static final Log LOG = LogFactory.getLog(FavoredNodeLoadBalancer.class);
private FavoredNodesPlan globalFavoredNodesAssignmentPlan;
private RackManager rackManager;
@Override
public void setConf(Configuration conf) {
super.setConf(conf);
globalFavoredNodesAssignmentPlan = new FavoredNodesPlan();
this.rackManager = new RackManager(conf);
super.setConf(conf);
}
@Override
public List<RegionPlan> balanceCluster(Map<ServerName, List<HRegionInfo>> clusterState) {
//TODO. Look at is whether Stochastic loadbalancer can be integrated with this
List<RegionPlan> plans = new ArrayList<RegionPlan>();
//perform a scan of the meta to get the latest updates (if any)
SnapshotOfRegionAssignmentFromMeta snaphotOfRegionAssignment =
new SnapshotOfRegionAssignmentFromMeta(super.services.getShortCircuitConnection());
try {
snaphotOfRegionAssignment.initialize();
} catch (IOException ie) {
LOG.warn("Not running balancer since exception was thrown " + ie);
return plans;
}
globalFavoredNodesAssignmentPlan = snaphotOfRegionAssignment.getExistingAssignmentPlan();
Map<ServerName, ServerName> serverNameToServerNameWithoutCode =
new HashMap<ServerName, ServerName>();
Map<ServerName, ServerName> serverNameWithoutCodeToServerName =
new HashMap<ServerName, ServerName>();
ServerManager serverMgr = super.services.getServerManager();
for (ServerName sn: serverMgr.getOnlineServersList()) {
ServerName s = ServerName.valueOf(sn.getHostname(), sn.getPort(), ServerName.NON_STARTCODE);
serverNameToServerNameWithoutCode.put(sn, s);
serverNameWithoutCodeToServerName.put(s, sn);
}
for (Map.Entry<ServerName, List<HRegionInfo>> entry : clusterState.entrySet()) {
ServerName currentServer = entry.getKey();
//get a server without the startcode for the currentServer
ServerName currentServerWithoutStartCode = ServerName.valueOf(currentServer.getHostname(),
currentServer.getPort(), ServerName.NON_STARTCODE);
List<HRegionInfo> list = entry.getValue();
for (HRegionInfo region : list) {
if(region.getTable().getNamespaceAsString()
.equals(NamespaceDescriptor.SYSTEM_NAMESPACE_NAME_STR)) {
continue;
}
List<ServerName> favoredNodes = globalFavoredNodesAssignmentPlan.getFavoredNodes(region);
if (favoredNodes == null || favoredNodes.get(0).equals(currentServerWithoutStartCode)) {
continue; //either favorednodes does not exist or we are already on the primary node
}
ServerName destination = null;
//check whether the primary is available
destination = serverNameWithoutCodeToServerName.get(favoredNodes.get(0));
if (destination == null) {
//check whether the region is on secondary/tertiary
if (currentServerWithoutStartCode.equals(favoredNodes.get(1)) ||
currentServerWithoutStartCode.equals(favoredNodes.get(2))) {
continue;
}
//the region is currently on none of the favored nodes
//get it on one of them if possible
ServerLoad l1 = super.services.getServerManager().getLoad(
serverNameWithoutCodeToServerName.get(favoredNodes.get(1)));
ServerLoad l2 = super.services.getServerManager().getLoad(
serverNameWithoutCodeToServerName.get(favoredNodes.get(2)));
if (l1 != null && l2 != null) {
if (l1.getLoad() > l2.getLoad()) {
destination = serverNameWithoutCodeToServerName.get(favoredNodes.get(2));
} else {
destination = serverNameWithoutCodeToServerName.get(favoredNodes.get(1));
}
} else if (l1 != null) {
destination = serverNameWithoutCodeToServerName.get(favoredNodes.get(1));
} else if (l2 != null) {
destination = serverNameWithoutCodeToServerName.get(favoredNodes.get(2));
}
}
if (destination != null) {
RegionPlan plan = new RegionPlan(region, currentServer, destination);
plans.add(plan);
}
}
}
return plans;
}
@Override
public Map<ServerName, List<HRegionInfo>> roundRobinAssignment(List<HRegionInfo> regions,
List<ServerName> servers) {
Map<ServerName, List<HRegionInfo>> assignmentMap;
try {
FavoredNodeAssignmentHelper assignmentHelper =
new FavoredNodeAssignmentHelper(servers, rackManager);
assignmentHelper.initialize();
if (!assignmentHelper.canPlaceFavoredNodes()) {
return super.roundRobinAssignment(regions, servers);
}
// Segregate the regions into two types:
// 1. The regions that have favored node assignment, and where at least
// one of the favored node is still alive. In this case, try to adhere
// to the current favored nodes assignment as much as possible - i.e.,
// if the current primary is gone, then make the secondary or tertiary
// as the new host for the region (based on their current load).
// Note that we don't change the favored
// node assignments here (even though one or more favored node is currently
// down). It is up to the balanceCluster to do this hard work. The HDFS
// can handle the fact that some nodes in the favored nodes hint is down
// It'd allocate some other DNs. In combination with stale settings for HDFS,
// we should be just fine.
// 2. The regions that currently don't have favored node assignment. We will
// need to come up with favored nodes assignments for them. The corner case
// in (1) above is that all the nodes are unavailable and in that case, we
// will note that this region doesn't have favored nodes.
Pair<Map<ServerName,List<HRegionInfo>>, List<HRegionInfo>> segregatedRegions =
segregateRegionsAndAssignRegionsWithFavoredNodes(regions, servers);
Map<ServerName,List<HRegionInfo>> regionsWithFavoredNodesMap = segregatedRegions.getFirst();
List<HRegionInfo> regionsWithNoFavoredNodes = segregatedRegions.getSecond();
assignmentMap = new HashMap<ServerName, List<HRegionInfo>>();
roundRobinAssignmentImpl(assignmentHelper, assignmentMap, regionsWithNoFavoredNodes,
servers);
// merge the assignment maps
assignmentMap.putAll(regionsWithFavoredNodesMap);
} catch (Exception ex) {
LOG.warn("Encountered exception while doing favored-nodes assignment " + ex +
" Falling back to regular assignment");
assignmentMap = super.roundRobinAssignment(regions, servers);
}
return assignmentMap;
}
@Override
public ServerName randomAssignment(HRegionInfo regionInfo, List<ServerName> servers) {
try {
FavoredNodeAssignmentHelper assignmentHelper =
new FavoredNodeAssignmentHelper(servers, rackManager);
assignmentHelper.initialize();
ServerName primary = super.randomAssignment(regionInfo, servers);
if (!assignmentHelper.canPlaceFavoredNodes()) {
return primary;
}
List<ServerName> favoredNodes = globalFavoredNodesAssignmentPlan.getFavoredNodes(regionInfo);
// check if we have a favored nodes mapping for this region and if so, return
// a server from the favored nodes list if the passed 'servers' contains this
// server as well (available servers, that is)
if (favoredNodes != null) {
for (ServerName s : favoredNodes) {
ServerName serverWithLegitStartCode = availableServersContains(servers, s);
if (serverWithLegitStartCode != null) {
return serverWithLegitStartCode;
}
}
}
List<HRegionInfo> regions = new ArrayList<HRegionInfo>(1);
regions.add(regionInfo);
Map<HRegionInfo, ServerName> primaryRSMap = new HashMap<HRegionInfo, ServerName>(1);
primaryRSMap.put(regionInfo, primary);
assignSecondaryAndTertiaryNodesForRegion(assignmentHelper, regions, primaryRSMap);
return primary;
} catch (Exception ex) {
LOG.warn("Encountered exception while doing favored-nodes (random)assignment " + ex +
" Falling back to regular assignment");
return super.randomAssignment(regionInfo, servers);
}
}
private Pair<Map<ServerName, List<HRegionInfo>>, List<HRegionInfo>>
segregateRegionsAndAssignRegionsWithFavoredNodes(List<HRegionInfo> regions,
List<ServerName> availableServers) {
Map<ServerName, List<HRegionInfo>> assignmentMapForFavoredNodes =
new HashMap<ServerName, List<HRegionInfo>>(regions.size() / 2);
List<HRegionInfo> regionsWithNoFavoredNodes = new ArrayList<HRegionInfo>(regions.size()/2);
for (HRegionInfo region : regions) {
List<ServerName> favoredNodes = globalFavoredNodesAssignmentPlan.getFavoredNodes(region);
ServerName primaryHost = null;
ServerName secondaryHost = null;
ServerName tertiaryHost = null;
if (favoredNodes != null) {
for (ServerName s : favoredNodes) {
ServerName serverWithLegitStartCode = availableServersContains(availableServers, s);
if (serverWithLegitStartCode != null) {
FavoredNodesPlan.Position position =
FavoredNodesPlan.getFavoredServerPosition(favoredNodes, s);
if (Position.PRIMARY.equals(position)) {
primaryHost = serverWithLegitStartCode;
} else if (Position.SECONDARY.equals(position)) {
secondaryHost = serverWithLegitStartCode;
} else if (Position.TERTIARY.equals(position)) {
tertiaryHost = serverWithLegitStartCode;
}
}
}
assignRegionToAvailableFavoredNode(assignmentMapForFavoredNodes, region,
primaryHost, secondaryHost, tertiaryHost);
}
if (primaryHost == null && secondaryHost == null && tertiaryHost == null) {
//all favored nodes unavailable
regionsWithNoFavoredNodes.add(region);
}
}
return new Pair<Map<ServerName, List<HRegionInfo>>, List<HRegionInfo>>(
assignmentMapForFavoredNodes, regionsWithNoFavoredNodes);
}
// Do a check of the hostname and port and return the servername from the servers list
// that matched (the favoredNode will have a startcode of -1 but we want the real
// server with the legit startcode
private ServerName availableServersContains(List<ServerName> servers, ServerName favoredNode) {
for (ServerName server : servers) {
if (ServerName.isSameHostnameAndPort(favoredNode, server)) {
return server;
}
}
return null;
}
private void assignRegionToAvailableFavoredNode(Map<ServerName,
List<HRegionInfo>> assignmentMapForFavoredNodes, HRegionInfo region, ServerName primaryHost,
ServerName secondaryHost, ServerName tertiaryHost) {
if (primaryHost != null) {
addRegionToMap(assignmentMapForFavoredNodes, region, primaryHost);
} else if (secondaryHost != null && tertiaryHost != null) {
// assign the region to the one with a lower load
// (both have the desired hdfs blocks)
ServerName s;
ServerLoad tertiaryLoad = super.services.getServerManager().getLoad(tertiaryHost);
ServerLoad secondaryLoad = super.services.getServerManager().getLoad(secondaryHost);
if (secondaryLoad.getLoad() < tertiaryLoad.getLoad()) {
s = secondaryHost;
} else {
s = tertiaryHost;
}
addRegionToMap(assignmentMapForFavoredNodes, region, s);
} else if (secondaryHost != null) {
addRegionToMap(assignmentMapForFavoredNodes, region, secondaryHost);
} else if (tertiaryHost != null) {
addRegionToMap(assignmentMapForFavoredNodes, region, tertiaryHost);
}
}
private void addRegionToMap(Map<ServerName, List<HRegionInfo>> assignmentMapForFavoredNodes,
HRegionInfo region, ServerName host) {
List<HRegionInfo> regionsOnServer = null;
if ((regionsOnServer = assignmentMapForFavoredNodes.get(host)) == null) {
regionsOnServer = new ArrayList<HRegionInfo>();
assignmentMapForFavoredNodes.put(host, regionsOnServer);
}
regionsOnServer.add(region);
}
public List<ServerName> getFavoredNodes(HRegionInfo regionInfo) {
return this.globalFavoredNodesAssignmentPlan.getFavoredNodes(regionInfo);
}
private void roundRobinAssignmentImpl(FavoredNodeAssignmentHelper assignmentHelper,
Map<ServerName, List<HRegionInfo>> assignmentMap,
List<HRegionInfo> regions, List<ServerName> servers) {
Map<HRegionInfo, ServerName> primaryRSMap = new HashMap<HRegionInfo, ServerName>();
// figure the primary RSs
assignmentHelper.placePrimaryRSAsRoundRobin(assignmentMap, primaryRSMap, regions);
assignSecondaryAndTertiaryNodesForRegion(assignmentHelper, regions, primaryRSMap);
}
private void assignSecondaryAndTertiaryNodesForRegion(
FavoredNodeAssignmentHelper assignmentHelper,
List<HRegionInfo> regions, Map<HRegionInfo, ServerName> primaryRSMap) {
// figure the secondary and tertiary RSs
Map<HRegionInfo, ServerName[]> secondaryAndTertiaryRSMap =
assignmentHelper.placeSecondaryAndTertiaryRS(primaryRSMap);
// now record all the assignments so that we can serve queries later
for (HRegionInfo region : regions) {
// Store the favored nodes without startCode for the ServerName objects
// We don't care about the startcode; but only the hostname really
List<ServerName> favoredNodesForRegion = new ArrayList<ServerName>(3);
ServerName sn = primaryRSMap.get(region);
favoredNodesForRegion.add(ServerName.valueOf(sn.getHostname(), sn.getPort(),
ServerName.NON_STARTCODE));
ServerName[] secondaryAndTertiaryNodes = secondaryAndTertiaryRSMap.get(region);
if (secondaryAndTertiaryNodes != null) {
favoredNodesForRegion.add(ServerName.valueOf(secondaryAndTertiaryNodes[0].getHostname(),
secondaryAndTertiaryNodes[0].getPort(), ServerName.NON_STARTCODE));
favoredNodesForRegion.add(ServerName.valueOf(secondaryAndTertiaryNodes[1].getHostname(),
secondaryAndTertiaryNodes[1].getPort(), ServerName.NON_STARTCODE));
}
globalFavoredNodesAssignmentPlan.updateFavoredNodesMap(region, favoredNodesForRegion);
}
}
}