| /* |
| * 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.accumulo.core.spi.balancer; |
| |
| import java.util.List; |
| import java.util.Map; |
| import java.util.Set; |
| import java.util.SortedMap; |
| |
| import org.apache.accumulo.core.conf.Property; |
| import org.apache.accumulo.core.data.TabletId; |
| import org.apache.accumulo.core.spi.balancer.data.TServerStatus; |
| import org.apache.accumulo.core.spi.balancer.data.TabletMigration; |
| import org.apache.accumulo.core.spi.balancer.data.TabletServerId; |
| |
| /** |
| * This class is responsible for managing the distribution of tablets throughout an Accumulo |
| * cluster. In most cases, users will want a balancer implementation which ensures a uniform |
| * distribution of tablets, so that no individual tablet server is handling significantly more work |
| * than any other. |
| * |
| * <p> |
| * Implementations may wish to store configuration in Accumulo's system configuration using the |
| * {@link Property#GENERAL_ARBITRARY_PROP_PREFIX}. They may also benefit from using per-table |
| * configuration using {@link Property#TABLE_ARBITRARY_PROP_PREFIX}. |
| * |
| * @since 2.1.0 |
| */ |
| public interface TabletBalancer { |
| |
| /** |
| * An interface for grouping parameters required for the balancer to assign unassigned tablets. |
| * This interface allows for evolution of the parameter set without changing the balancer's method |
| * signature. |
| * |
| * @since 2.1.0 |
| */ |
| interface AssignmentParameters { |
| /** |
| * @return the current status for all tablet servers (read-only) |
| */ |
| SortedMap<TabletServerId,TServerStatus> currentStatus(); |
| |
| /** |
| * @return the tablets that need to be assigned, mapped to their previous known location |
| * (read-only) |
| */ |
| Map<TabletId,TabletServerId> unassignedTablets(); |
| |
| /** |
| * Assigns {@code tabletId} to {@code tabletServerId}. |
| */ |
| void addAssignment(TabletId tabletId, TabletServerId tabletServerId); |
| } |
| |
| /** |
| * An interface for grouping parameters required for the balancer to balance tablets. This |
| * interface allows for evolution of the parameter set without changing the balancer's method |
| * signature. |
| * |
| * @since 2.1.0 |
| */ |
| interface BalanceParameters { |
| /** |
| * @return the current status for all tablet servers (read-only) |
| */ |
| SortedMap<TabletServerId,TServerStatus> currentStatus(); |
| |
| /** |
| * @return the migrations that are currently in progress (read-only) |
| */ |
| Set<TabletId> currentMigrations(); |
| |
| /** |
| * @return a write-only map for storing new assignments made by the balancer. It is important |
| * that any tablets found in {@link #currentMigrations()} are not included in the output |
| * migrations. |
| */ |
| List<TabletMigration> migrationsOut(); |
| } |
| |
| /** |
| * Initialize the TabletBalancer. This gives the balancer the opportunity to read the |
| * configuration. |
| */ |
| void init(BalancerEnvironment balancerEnvironment); |
| |
| /** |
| * Assign tablets to tablet servers. This method is called whenever the manager finds tablets that |
| * are unassigned. |
| */ |
| void getAssignments(AssignmentParameters params); |
| |
| /** |
| * Ask the balancer if any migrations are necessary. |
| * |
| * If the balancer is going to self-abort due to some environmental constraint (e.g. it requires |
| * some minimum number of tservers, or a maximum number of outstanding migrations), it should |
| * issue a log message to alert operators. The message should be at WARN normally and at ERROR if |
| * the balancer knows that the problem can not self correct. It should not issue these messages |
| * more than once a minute. This method will not be called when there are unassigned tablets. |
| * |
| * @return the time, in milliseconds, to wait before re-balancing. |
| */ |
| long balance(BalanceParameters params); |
| } |