Decouple shard allocation awareness from search and get requests (#45735)

jimczi · web-flow · commit a4ed7b1ca102 · 2019-09-04T21:48:03.000+02:00
With this commit, Elasticsearch will no longer prefer using shards in the same location (with the same awareness attribute values) to process `_search` and `_get` requests. Instead, adaptive replica selection (the default since 7.0) should route requests more efficiently using the service time of prior inter-node communications. Clusters with big latencies between nodes should switch to cross cluster replication to isolate nodes within the same zone. Note that this change only targets 8.0 since it is considered as breaking. However a follow up pr should add an option to activate this behavior in 7.x in order to allow users to opt-in early. Closes #43453
diff --git a/docs/reference/migration/migrate_8_0/search.asciidoc b/docs/reference/migration/migrate_8_0/search.asciidoc
@@ -12,16 +12,24 @@ The `/{index}/{type}/_termvectors`, `/{index}/{type}/{id}/_termvectors` and `/{i
 [float]
 ==== Removal of queries
 
-The `common` query was deprecated in 7.x and  has been removed in 8.0.
+The `common` query, deprecated in 7.x, has been removed in 8.0.
 The same functionality can be achieved by the `match` query if the total number of hits is not tracked.
 
 [float]
 ===== Removal of query parameters
 
-The `cutoff_frequency` parameter was deprecated in 7.x and has been removed in 8.0 from `match` and `multi_match` queries.
+The `cutoff_frequency` parameter, deprecated in 7.x, has been removed in 8.0 from `match` and `multi_match` queries.
 The same functionality can be achieved without any configuration provided that the total number of hits is not tracked.
 
 [float]
 ===== Removal of sort parameters
 
 The `nested_filter` and `nested_path` options, deprecated in 6.x, have been removed in favor of the `nested` context.
+
+
+[float]
+===== Shard allocation awareness in Search and Get requests
+
+{es} will no longer prefer using shards in the same location (with the same awareness attribute values) to process
+`_search` and `_get` requests. Adaptive replica selection (activated by default in this version) will route requests
+more efficiently using the service time of prior inter-node communications.
diff --git a/docs/reference/modules/cluster/allocation_awareness.asciidoc b/docs/reference/modules/cluster/allocation_awareness.asciidoc
@@ -17,10 +17,6 @@ The allocation awareness settings can be configured in
 `elasticsearch.yml` and updated dynamically with the
 <<cluster-update-settings,cluster-update-settings>> API.
 
-{es} prefers using shards in the same location (with the same
-awareness attribute values) to process search or GET requests. Using local
-shards is usually faster than crossing rack or zone boundaries.
-
 NOTE: The number of attribute values determines how many shard copies are
 allocated in each location. If the number of nodes in each location is
 unbalanced and there are a lot of replicas, replica shards might be left
diff --git a/server/src/main/java/org/elasticsearch/cluster/routing/IndexShardRoutingTable.java b/server/src/main/java/org/elasticsearch/cluster/routing/IndexShardRoutingTable.java
@@ -19,13 +19,11 @@
 
 package org.elasticsearch.cluster.routing;
 
-import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Randomness;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.util.Maps;
 import org.elasticsearch.common.util.set.Sets;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.shard.ShardId;
@@ -44,8 +42,6 @@
 import java.util.Optional;
 import java.util.Set;
 
-import static java.util.Collections.emptyMap;
-
 /**
  * {@link IndexShardRoutingTable} encapsulates all instances of a single shard.
  * Each Elasticsearch index consists of multiple shards, each shard encapsulates
@@ -67,10 +63,6 @@ public class IndexShardRoutingTable implements Iterable<ShardRouting> {
     final Set<String> allAllocationIds;
     final boolean allShardsStarted;
 
-    private volatile Map<AttributesKey, AttributesRoutings> activeShardsByAttributes = emptyMap();
-    private volatile Map<AttributesKey, AttributesRoutings> initializingShardsByAttributes = emptyMap();
-    private final Object shardsByAttributeMutex = new Object();
-
     /**
      * The initializing list, including ones that are initializing on a target node because of relocation.
      * If we can come up with a better variable name, it would be nice...
@@ -549,86 +541,6 @@ public boolean equals(Object obj) {
         }
     }
 
-    static class AttributesRoutings {
-
-        public final List<ShardRouting> withSameAttribute;
-        public final List<ShardRouting> withoutSameAttribute;
-        public final int totalSize;
-
-        AttributesRoutings(List<ShardRouting> withSameAttribute, List<ShardRouting> withoutSameAttribute) {
-            this.withSameAttribute = withSameAttribute;
-            this.withoutSameAttribute = withoutSameAttribute;
-            this.totalSize = withoutSameAttribute.size() + withSameAttribute.size();
-        }
-    }
-
-    private AttributesRoutings getActiveAttribute(AttributesKey key, DiscoveryNodes nodes) {
-        AttributesRoutings shardRoutings = activeShardsByAttributes.get(key);
-        if (shardRoutings == null) {
-            synchronized (shardsByAttributeMutex) {
-                ArrayList<ShardRouting> from = new ArrayList<>(activeShards);
-                List<ShardRouting> to = collectAttributeShards(key, nodes, from);
-
-                shardRoutings = new AttributesRoutings(to, Collections.unmodifiableList(from));
-                activeShardsByAttributes = Maps.copyMapWithAddedEntry(activeShardsByAttributes, key, shardRoutings);
-            }
-        }
-        return shardRoutings;
-    }
-
-    private AttributesRoutings getInitializingAttribute(AttributesKey key, DiscoveryNodes nodes) {
-        AttributesRoutings shardRoutings = initializingShardsByAttributes.get(key);
-        if (shardRoutings == null) {
-            synchronized (shardsByAttributeMutex) {
-                ArrayList<ShardRouting> from = new ArrayList<>(allInitializingShards);
-                List<ShardRouting> to = collectAttributeShards(key, nodes, from);
-                shardRoutings = new AttributesRoutings(to, Collections.unmodifiableList(from));
-                initializingShardsByAttributes =
-                        Maps.copyMapWithAddedEntry(initializingShardsByAttributes, key, shardRoutings);
-            }
-        }
-        return shardRoutings;
-    }
-
-    private static List<ShardRouting> collectAttributeShards(AttributesKey key, DiscoveryNodes nodes, ArrayList<ShardRouting> from) {
-        final ArrayList<ShardRouting> to = new ArrayList<>();
-        for (final String attribute : key.attributes) {
-            final String localAttributeValue = nodes.getLocalNode().getAttributes().get(attribute);
-            if (localAttributeValue != null) {
-                for (Iterator<ShardRouting> iterator = from.iterator(); iterator.hasNext(); ) {
-                    ShardRouting fromShard = iterator.next();
-                    final DiscoveryNode discoveryNode = nodes.get(fromShard.currentNodeId());
-                    if (discoveryNode == null) {
-                        iterator.remove(); // node is not present anymore - ignore shard
-                    } else if (localAttributeValue.equals(discoveryNode.getAttributes().get(attribute))) {
-                        iterator.remove();
-                        to.add(fromShard);
-                    }
-                }
-            }
-        }
-        return Collections.unmodifiableList(to);
-    }
-
-    public ShardIterator preferAttributesActiveInitializingShardsIt(List<String> attributes, DiscoveryNodes nodes) {
-        return preferAttributesActiveInitializingShardsIt(attributes, nodes, shuffler.nextSeed());
-    }
-
-    public ShardIterator preferAttributesActiveInitializingShardsIt(List<String> attributes, DiscoveryNodes nodes, int seed) {
-        AttributesKey key = new AttributesKey(attributes);
-        AttributesRoutings activeRoutings = getActiveAttribute(key, nodes);
-        AttributesRoutings initializingRoutings = getInitializingAttribute(key, nodes);
-
-        // we now randomize, once between the ones that have the same attributes, and once for the ones that don't
-        // we don't want to mix between the two!
-        ArrayList<ShardRouting> ordered = new ArrayList<>(activeRoutings.totalSize + initializingRoutings.totalSize);
-        ordered.addAll(shuffler.shuffle(activeRoutings.withSameAttribute, seed));
-        ordered.addAll(shuffler.shuffle(activeRoutings.withoutSameAttribute, seed));
-        ordered.addAll(shuffler.shuffle(initializingRoutings.withSameAttribute, seed));
-        ordered.addAll(shuffler.shuffle(initializingRoutings.withoutSameAttribute, seed));
-        return new PlainShardIterator(shardId, ordered);
-    }
-
     public ShardRouting primaryShard() {
         return primary;
     }
diff --git a/server/src/main/java/org/elasticsearch/cluster/routing/OperationRouting.java b/server/src/main/java/org/elasticsearch/cluster/routing/OperationRouting.java
@@ -22,7 +22,6 @@
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
-import org.elasticsearch.cluster.routing.allocation.decider.AwarenessAllocationDecider;
 import org.elasticsearch.common.Nullable;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.settings.ClusterSettings;
@@ -36,7 +35,6 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
-import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.stream.Collectors;
@@ -47,25 +45,17 @@ public class OperationRouting {
             Setting.boolSetting("cluster.routing.use_adaptive_replica_selection", true,
                     Setting.Property.Dynamic, Setting.Property.NodeScope);
 
-    private List<String> awarenessAttributes;
     private boolean useAdaptiveReplicaSelection;
 
     public OperationRouting(Settings settings, ClusterSettings clusterSettings) {
-        this.awarenessAttributes = AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING.get(settings);
         this.useAdaptiveReplicaSelection = USE_ADAPTIVE_REPLICA_SELECTION_SETTING.get(settings);
-        clusterSettings.addSettingsUpdateConsumer(AwarenessAllocationDecider.CLUSTER_ROUTING_ALLOCATION_AWARENESS_ATTRIBUTE_SETTING,
-            this::setAwarenessAttributes);
         clusterSettings.addSettingsUpdateConsumer(USE_ADAPTIVE_REPLICA_SELECTION_SETTING, this::setUseAdaptiveReplicaSelection);
     }
 
     void setUseAdaptiveReplicaSelection(boolean useAdaptiveReplicaSelection) {
         this.useAdaptiveReplicaSelection = useAdaptiveReplicaSelection;
     }
 
-    private void setAwarenessAttributes(List<String> awarenessAttributes) {
-        this.awarenessAttributes = awarenessAttributes;
-    }
-
     public ShardIterator indexShards(ClusterState clusterState, String index, String id, @Nullable String routing) {
         return shards(clusterState, index, id, routing).shardsIt();
     }
@@ -194,23 +184,15 @@ private ShardIterator preferenceActiveShardIterator(IndexShardRoutingTable index
         }
         // if not, then use it as the index
         int routingHash = 31 * Murmur3HashFunction.hash(preference) + indexShard.shardId.hashCode();
-        if (awarenessAttributes.isEmpty()) {
-            return indexShard.activeInitializingShardsIt(routingHash);
-        } else {
-            return indexShard.preferAttributesActiveInitializingShardsIt(awarenessAttributes, nodes, routingHash);
-        }
+        return indexShard.activeInitializingShardsIt(routingHash);
     }
 
     private ShardIterator shardRoutings(IndexShardRoutingTable indexShard, DiscoveryNodes nodes,
             @Nullable ResponseCollectorService collectorService, @Nullable Map<String, Long> nodeCounts) {
-        if (awarenessAttributes.isEmpty()) {
-            if (useAdaptiveReplicaSelection) {
-                return indexShard.activeInitializingShardsRankedIt(collectorService, nodeCounts);
-            } else {
-                return indexShard.activeInitializingShardsRandomIt();
-            }
+        if (useAdaptiveReplicaSelection) {
+            return indexShard.activeInitializingShardsRankedIt(collectorService, nodeCounts);
         } else {
-            return indexShard.preferAttributesActiveInitializingShardsIt(awarenessAttributes, nodes);
+            return indexShard.activeInitializingShardsRandomIt();
         }
     }
 
diff --git a/server/src/test/java/org/elasticsearch/cluster/structure/RoutingIteratorTests.java b/server/src/test/java/org/elasticsearch/cluster/structure/RoutingIteratorTests.java
@@ -41,10 +41,8 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.shard.ShardId;
 
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.Iterator;
-import java.util.Map;
 
 import static java.util.Collections.singletonMap;
 import static org.hamcrest.Matchers.anyOf;
@@ -224,59 +222,6 @@ public void testRandomRouting() {
         assertThat(shardRouting1, sameInstance(shardRouting3));
     }
 
-    public void testAttributePreferenceRouting() {
-        Settings.Builder settings = Settings.builder()
-            .put("cluster.routing.allocation.node_concurrent_recoveries", 10)
-            .put(ClusterRebalanceAllocationDecider.CLUSTER_ROUTING_ALLOCATION_ALLOW_REBALANCE_SETTING.getKey(), "always");
-        if (randomBoolean()) {
-            settings.put("cluster.routing.allocation.awareness.attributes", " rack_id, zone  ");
-        } else {
-            settings.putList("cluster.routing.allocation.awareness.attributes", "rack_id", "zone");
-        }
-
-        AllocationService strategy = createAllocationService(settings.build());
-
-        MetaData metaData = MetaData.builder()
-                .put(IndexMetaData.builder("test").settings(settings(Version.CURRENT)).numberOfShards(1).numberOfReplicas(1))
-                .build();
-
-        RoutingTable routingTable = RoutingTable.builder()
-                .addAsNew(metaData.index("test"))
-                .build();
-
-        ClusterState clusterState = ClusterState.builder(ClusterName.CLUSTER_NAME_SETTING
-            .getDefault(Settings.EMPTY)).metaData(metaData).routingTable(routingTable).build();
-
-        clusterState = ClusterState.builder(clusterState).nodes(DiscoveryNodes.builder()
-                .add(newNode("node1", Map.of("rack_id", "rack_1", "zone", "zone1")))
-                .add(newNode("node2", Map.of("rack_id", "rack_2", "zone", "zone2")))
-                .localNodeId("node1")
-        ).build();
-        clusterState = strategy.reroute(clusterState, "reroute");
-
-        clusterState = startInitializingShardsAndReroute(strategy, clusterState);
-        clusterState = startInitializingShardsAndReroute(strategy, clusterState);
-
-        // after all are started, check routing iteration
-        ShardIterator shardIterator = clusterState.routingTable().index("test").shard(0)
-            .preferAttributesActiveInitializingShardsIt(Arrays.asList("rack_id"), clusterState.nodes());
-        ShardRouting shardRouting = shardIterator.nextOrNull();
-        assertThat(shardRouting, notNullValue());
-        assertThat(shardRouting.currentNodeId(), equalTo("node1"));
-        shardRouting = shardIterator.nextOrNull();
-        assertThat(shardRouting, notNullValue());
-        assertThat(shardRouting.currentNodeId(), equalTo("node2"));
-
-        shardIterator = clusterState.routingTable().index("test").shard(0)
-            .preferAttributesActiveInitializingShardsIt(Arrays.asList("rack_id"), clusterState.nodes());
-        shardRouting = shardIterator.nextOrNull();
-        assertThat(shardRouting, notNullValue());
-        assertThat(shardRouting.currentNodeId(), equalTo("node1"));
-        shardRouting = shardIterator.nextOrNull();
-        assertThat(shardRouting, notNullValue());
-        assertThat(shardRouting.currentNodeId(), equalTo("node2"));
-    }
-
     public void testNodeSelectorRouting(){
         AllocationService strategy = createAllocationService(Settings.builder()
                 .put("cluster.routing.allocation.node_concurrent_recoveries", 10)
