/
ShardsAllocator.java
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/
ShardsAllocator.java
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/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.cluster.routing.allocation.allocator;
import org.elasticsearch.cluster.routing.MutableShardRouting;
import org.elasticsearch.cluster.routing.RoutingNode;
import org.elasticsearch.cluster.routing.ShardRouting;
import org.elasticsearch.cluster.routing.ShardRoutingState;
import org.elasticsearch.cluster.routing.allocation.FailedRerouteAllocation;
import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
import org.elasticsearch.cluster.routing.allocation.StartedRerouteAllocation;
/**
* <p>
* A {@link ShardsAllocator} is the main entry point for shard allocation on nodes in the cluster.
* The allocator makes basic decision where a shard instance will be allocated, if already allocated instances
* need relocate to other nodes due to node failures or due to rebalancing decisions.
* </p>
*/
public interface ShardsAllocator {
/**
* Applies changes on started nodes based on the implemented algorithm. For example if a
* shard has changed to {@link ShardRoutingState#STARTED} from {@link ShardRoutingState#RELOCATING}
* this allocator might apply some cleanups on the node that used to hold the shard.
* @param allocation all started {@link ShardRouting shards}
*/
void applyStartedShards(StartedRerouteAllocation allocation);
/**
* Applies changes on failed nodes based on the implemented algorithm.
* @param allocation all failed {@link ShardRouting shards}
*/
void applyFailedShards(FailedRerouteAllocation allocation);
/**
* Assign all unassigned shards to nodes
*
* @param allocation current node allocation
* @return <code>true</code> if the allocation has changed, otherwise <code>false</code>
*/
boolean allocateUnassigned(RoutingAllocation allocation);
/**
* Rebalancing number of shards on all nodes
*
* @param allocation current node allocation
* @return <code>true</code> if the allocation has changed, otherwise <code>false</code>
*/
boolean rebalance(RoutingAllocation allocation);
/**
* Moves a shard from the given node to other node.
*
* @param shardRouting the shard to move
* @param node A node containing the shard
* @param allocation current node allocation
* @return <code>true</code> if the allocation has changed, otherwise <code>false</code>
*/
boolean move(MutableShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation);
}