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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.
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package org.elasticsearch.cluster.routing.allocation.decider;

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.RoutingAllocation;
import org.elasticsearch.common.inject.Inject;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.node.settings.NodeSettingsService;

/**
 * {@link ThrottlingAllocationDecider} controls the recovery process per node in
 * the cluster. It exposes two settings via the cluster update API that allow
 * changes in real-time:
 * <p/>
 * <ul>
 * <li><tt>cluster.routing.allocation.node_initial_primaries_recoveries</tt> -
 * restricts the number of initial primary shard recovery operations on a single
 * node. The default is <tt>4</tt></li>
 * <p/>
 * <li><tt>cluster.routing.allocation.node_concurrent_recoveries</tt> -
 * restricts the number of concurrent recovery operations on a single node. The
 * default is <tt>2</tt></li>
 * </ul>
 * <p/>
 * If one of the above thresholds is exceeded per node this allocation decider
 * will return {@link Decision#THROTTLE} as a hit to upstream logic to throttle
 * the allocation process to prevent overloading nodes due to too many concurrent recovery
 * processes.
 */
public class ThrottlingAllocationDecider extends AllocationDecider {

    public static final String NAME = "throttling";

    public static final String CLUSTER_ROUTING_ALLOCATION_NODE_INITIAL_PRIMARIES_RECOVERIES = "cluster.routing.allocation.node_initial_primaries_recoveries";
    public static final String CLUSTER_ROUTING_ALLOCATION_NODE_CONCURRENT_RECOVERIES = "cluster.routing.allocation.node_concurrent_recoveries";
    public static final String CLUSTER_ROUTING_ALLOCATION_CONCURRENT_RECOVERIES = "cluster.routing.allocation.concurrent_recoveries";

    public static final int DEFAULT_CLUSTER_ROUTING_ALLOCATION_NODE_CONCURRENT_RECOVERIES = 2;
    public static final int DEFAULT_CLUSTER_ROUTING_ALLOCATION_NODE_INITIAL_PRIMARIES_RECOVERIES = 4;

    private volatile int primariesInitialRecoveries;
    private volatile int concurrentRecoveries;

    @Inject
    public ThrottlingAllocationDecider(Settings settings, NodeSettingsService nodeSettingsService) {
        super(settings);

        this.primariesInitialRecoveries = settings.getAsInt(CLUSTER_ROUTING_ALLOCATION_NODE_INITIAL_PRIMARIES_RECOVERIES, DEFAULT_CLUSTER_ROUTING_ALLOCATION_NODE_INITIAL_PRIMARIES_RECOVERIES);
        this.concurrentRecoveries = settings.getAsInt(CLUSTER_ROUTING_ALLOCATION_CONCURRENT_RECOVERIES, settings.getAsInt(CLUSTER_ROUTING_ALLOCATION_NODE_CONCURRENT_RECOVERIES, DEFAULT_CLUSTER_ROUTING_ALLOCATION_NODE_CONCURRENT_RECOVERIES));
        logger.debug("using node_concurrent_recoveries [{}], node_initial_primaries_recoveries [{}]", concurrentRecoveries, primariesInitialRecoveries);

        nodeSettingsService.addListener(new ApplySettings());
    }

    @Override
    public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) {
        if (shardRouting.primary()) {
            assert shardRouting.unassigned() || shardRouting.active();
            if (shardRouting.unassigned()) {
                // primary is unassigned, means we are going to do recovery from gateway
                // count *just the primary* currently doing recovery on the node and check against concurrent_recoveries
                int primariesInRecovery = 0;
                for (MutableShardRouting shard : node) {
                    // when a primary shard is INITIALIZING, it can be because of *initial recovery* or *relocation from another node*
                    // we only count initial recoveries here, so we need to make sure that relocating node is null
                    if (shard.state() == ShardRoutingState.INITIALIZING && shard.primary() && shard.relocatingNodeId() == null) {
                        primariesInRecovery++;
                    }
                }
                if (primariesInRecovery >= primariesInitialRecoveries) {
                    return allocation.decision(Decision.THROTTLE, NAME, "too many primaries currently recovering [%d], limit: [%d]",
                            primariesInRecovery, primariesInitialRecoveries);
                } else {
                    return allocation.decision(Decision.YES, NAME, "below primary recovery limit of [%d]", primariesInitialRecoveries);
                }
            }
        }

        // either primary or replica doing recovery (from peer shard)

        // count the number of recoveries on the node, its for both target (INITIALIZING) and source (RELOCATING)
        return canAllocate(node, allocation);
    }

    public Decision canAllocate(RoutingNode node, RoutingAllocation allocation) {
        int currentRecoveries = 0;
        for (MutableShardRouting shard : node) {
            if (shard.state() == ShardRoutingState.INITIALIZING || shard.state() == ShardRoutingState.RELOCATING) {
                currentRecoveries++;
            }
        }
        if (currentRecoveries >= concurrentRecoveries) {
            return allocation.decision(Decision.THROTTLE, NAME, "too many shards currently recovering [%d], limit: [%d]",
                    currentRecoveries, concurrentRecoveries);
        } else {
            return allocation.decision(Decision.YES, NAME, "below shard recovery limit of [%d]", concurrentRecoveries);
        }
    }

    class ApplySettings implements NodeSettingsService.Listener {
        @Override
        public void onRefreshSettings(Settings settings) {
            int primariesInitialRecoveries = settings.getAsInt(CLUSTER_ROUTING_ALLOCATION_NODE_INITIAL_PRIMARIES_RECOVERIES, ThrottlingAllocationDecider.this.primariesInitialRecoveries);
            if (primariesInitialRecoveries != ThrottlingAllocationDecider.this.primariesInitialRecoveries) {
                logger.info("updating [cluster.routing.allocation.node_initial_primaries_recoveries] from [{}] to [{}]", ThrottlingAllocationDecider.this.primariesInitialRecoveries, primariesInitialRecoveries);
                ThrottlingAllocationDecider.this.primariesInitialRecoveries = primariesInitialRecoveries;
            }

            int concurrentRecoveries = settings.getAsInt(CLUSTER_ROUTING_ALLOCATION_NODE_CONCURRENT_RECOVERIES, ThrottlingAllocationDecider.this.concurrentRecoveries);
            if (concurrentRecoveries != ThrottlingAllocationDecider.this.concurrentRecoveries) {
                logger.info("updating [cluster.routing.allocation.node_concurrent_recoveries] from [{}] to [{}]", ThrottlingAllocationDecider.this.concurrentRecoveries, concurrentRecoveries);
                ThrottlingAllocationDecider.this.concurrentRecoveries = concurrentRecoveries;
            }
        }
    }
}
