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/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

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

import org.elasticsearch.cluster.metadata.IndexMetadata;
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.settings.ClusterSettings;
import org.elasticsearch.common.settings.Setting;
import org.elasticsearch.common.settings.Setting.Property;
import org.elasticsearch.common.settings.Settings;

import java.util.function.BiPredicate;

/**
 * This {@link AllocationDecider} limits the number of shards per node on a per
 * index or node-wide basis. The allocator prevents a single node to hold more
 * than {@code index.routing.allocation.total_shards_per_node} per index and
 * {@code cluster.routing.allocation.total_shards_per_node} globally during the allocation
 * process. The limits of this decider can be changed in real-time via a the
 * index settings API.
 * 

* If {@code index.routing.allocation.total_shards_per_node} is reset to a negative value shards * per index are unlimited per node. Shards currently in the * {@link ShardRoutingState#RELOCATING relocating} state are ignored by this * {@link AllocationDecider} until the shard changed its state to either * {@link ShardRoutingState#STARTED started}, * {@link ShardRoutingState#INITIALIZING inializing} or * {@link ShardRoutingState#UNASSIGNED unassigned} *

* Note: Reducing the number of shards per node via the index update API can * trigger relocation and significant additional load on the clusters nodes. *

*/ public class ShardsLimitAllocationDecider extends AllocationDecider { public static final String NAME = "shards_limit"; private volatile int clusterShardLimit; /** * Controls the maximum number of shards per index on a single Elasticsearch * node. Negative values are interpreted as unlimited. */ public static final Setting INDEX_TOTAL_SHARDS_PER_NODE_SETTING = Setting.intSetting("index.routing.allocation.total_shards_per_node", -1, -1, Property.Dynamic, Property.IndexScope); /** * Controls the maximum number of shards per node on a global level. * Negative values are interpreted as unlimited. */ public static final Setting CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING = Setting.intSetting("cluster.routing.allocation.total_shards_per_node", -1, -1, Property.Dynamic, Property.NodeScope); private final Settings settings; public ShardsLimitAllocationDecider(Settings settings, ClusterSettings clusterSettings) { this.settings = settings; this.clusterShardLimit = CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING.get(settings); clusterSettings.addSettingsUpdateConsumer(CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING, this::setClusterShardLimit); } private void setClusterShardLimit(int clusterShardLimit) { this.clusterShardLimit = clusterShardLimit; } @Override public Decision canAllocate(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) { return doDecide(shardRouting, node, allocation, (count, limit) -> count >= limit); } @Override public Decision canRemain(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation) { return doDecide(shardRouting, node, allocation, (count, limit) -> count > limit); } private Decision doDecide(ShardRouting shardRouting, RoutingNode node, RoutingAllocation allocation, BiPredicate decider) { IndexMetadata indexMd = allocation.metadata().getIndexSafe(shardRouting.index()); final int indexShardLimit = INDEX_TOTAL_SHARDS_PER_NODE_SETTING.get(indexMd.getSettings(), settings); // Capture the limit here in case it changes during this method's // execution final int clusterShardLimit = this.clusterShardLimit; if (indexShardLimit <= 0 && clusterShardLimit <= 0) { return allocation.decision(Decision.YES, NAME, "total shard limits are disabled: [index: %d, cluster: %d] <= 0", indexShardLimit, clusterShardLimit); } final int nodeShardCount = node.numberOfOwningShards(); if (clusterShardLimit > 0 && decider.test(nodeShardCount, clusterShardLimit)) { return allocation.decision(Decision.NO, NAME, "too many shards [%d] allocated to this node, cluster setting [%s=%d]", nodeShardCount, CLUSTER_TOTAL_SHARDS_PER_NODE_SETTING.getKey(), clusterShardLimit); } if (indexShardLimit > 0) { final int indexShardCount = node.numberOfOwningShardsForIndex(shardRouting.index()); if (decider.test(indexShardCount, indexShardLimit)) { return allocation.decision(Decision.NO, NAME, "too many shards [%d] allocated to this node for index [%s], index setting [%s=%d]", indexShardCount, shardRouting.getIndexName(), INDEX_TOTAL_SHARDS_PER_NODE_SETTING.getKey(), indexShardLimit); } } return allocation.decision(Decision.YES, NAME, "the shard count [%d] for this node is under the index limit [%d] and cluster level node limit [%d]", nodeShardCount, indexShardLimit, clusterShardLimit); } }




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