[GitHub] [lucene-solr] noblepaul commented on a change in pull request #2187: SOLR-15052 Reducing overseer bottlenecks using per-replica states (8x)

[GitBox <gi...@apache.org>]

noblepaul commented on a change in pull request #2187:
URL: https://github.com/apache/lucene-solr/pull/2187#discussion_r554294274



##########
File path: solr/solrj/src/java/org/apache/solr/common/cloud/PerReplicaStates.java
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@@ -0,0 +1,310 @@
+/*
+ * 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.solr.common.cloud;
+
+import java.io.IOException;
+import java.lang.invoke.MethodHandles;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.function.BiConsumer;
+
+import org.apache.solr.cluster.api.SimpleMap;
+import org.apache.solr.common.MapWriter;
+import org.apache.solr.common.SolrException;
+import org.apache.solr.common.annotation.JsonProperty;
+import org.apache.solr.common.util.ReflectMapWriter;
+import org.apache.solr.common.util.StrUtils;
+import org.apache.solr.common.util.WrappedSimpleMap;
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.data.Stat;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static org.apache.solr.common.params.CommonParams.NAME;
+import static org.apache.solr.common.params.CommonParams.VERSION;
+
+/**
+ * This represents the individual replica states in a collection
+ * This is an immutable object. When states are modified, a new instance is constructed
+ */
+public class PerReplicaStates implements ReflectMapWriter {
+  private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+  public static final char SEPARATOR = ':';
+  //no:of times to retry in case of a CAS failure
+  public static final int MAX_RETRIES = 5;
+
+
+  @JsonProperty
+  public final String path;
+
+  @JsonProperty
+  public final int cversion;
+
+  @JsonProperty
+  public final SimpleMap<State> states;
+
+  /**
+   * Construct with data read from ZK
+   * @param path path from where this is loaded
+   * @param cversion the current child version of the znode
+   * @param states the per-replica states (the list of all child nodes)
+   */
+  public PerReplicaStates(String path, int cversion, List<String> states) {
+    this.path = path;
+    this.cversion = cversion;
+    Map<String, State> tmp = new LinkedHashMap<>();
+
+    for (String state : states) {
+      State rs = State.parse(state);
+      if (rs == null) continue;
+      State existing = tmp.get(rs.replica);
+      if (existing == null) {
+        tmp.put(rs.replica, rs);
+      } else {
+        tmp.put(rs.replica, rs.insert(existing));
+      }
+    }
+    this.states = new WrappedSimpleMap<>(tmp);
+
+  }
+
+  /**Get the changed replicas
+   */
+  public static Set<String> findModifiedReplicas(PerReplicaStates old, PerReplicaStates fresh) {
+    Set<String> result = new HashSet<>();
+    if (fresh == null) {
+      old.states.forEachKey(result::add);
+      return result;
+    }
+    old.states.forEachEntry((s, state) -> {
+      // the state is modified or missing
+      if (!Objects.equals(fresh.get(s) , state)) result.add(s);
+    });
+    fresh.states.forEachEntry((s, state) -> { if (old.get(s) == null ) result.add(s);
+    });
+    return result;
+  }
+
+
+  /**
+   * Fetch the latest {@link PerReplicaStates} . It fetches data after checking the {@link Stat#getCversion()} of state.json.
+   * If this is not modified, the same object is returned
+   */
+  public static PerReplicaStates fetch(String path, SolrZkClient zkClient, PerReplicaStates current) {
+    try {
+      if (current != null) {
+        Stat stat = zkClient.exists(current.path, null, true);
+        if (stat == null) return new PerReplicaStates(path, -1, Collections.emptyList());
+        if (current.cversion == stat.getCversion()) return current;// not modifiedZkStateReaderTest
+      }
+      Stat stat = new Stat();
+      List<String> children = zkClient.getChildren(path, null, stat, true);
+      return new PerReplicaStates(path, stat.getCversion(), Collections.unmodifiableList(children));
+    } catch (KeeperException e) {
+      throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "Error fetching per-replica states", e);
+    } catch (InterruptedException e) {
+      SolrZkClient.checkInterrupted(e);
+      throw new SolrException(SolrException.ErrorCode.SERVER_ERROR, "Thread interrupted when loading per-replica states from " + path, e);
+    }
+  }
+
+
+  public static String getReplicaName(String s) {
+    int idx = s.indexOf(SEPARATOR);
+    if (idx > 0) {
+      return s.substring(0, idx);
+    }
+    return null;
+  }
+
+  public State get(String replica) {
+    return states.get(replica);
+  }
+
+  public static class Operation {
+    public final Type typ;
+    public final State state;
+
+    public Operation(Type typ, State replicaState) {
+      this.typ = typ;
+      this.state = replicaState;
+    }
+
+
+    public enum Type {
+      //add a new node
+      ADD,
+      //delete an existing node
+      DELETE
+    }
+
+    @Override
+    public String toString() {
+      return typ.toString() + " : " + state;
+    }
+  }
+
+
+  /**
+   * The state of a replica as stored as a node under /collections/collection-name/state.json/replica-state
+   */
+  public static class State implements MapWriter {
+
+    public final String replica;
+
+    public final Replica.State state;
+
+    public final Boolean isLeader;
+
+    public final int version;
+
+    public final String asString;
+
+    /**
+     * if there are multiple entries for the same replica, e.g: core_node_1:12:A core_node_1:13:D
+     * <p>
+     * the entry with '13' is the latest and the one with '12' is considered a duplicate
+     * <p>
+     * These are unlikely, but possible
+     */
+    final State duplicate;

Review comment:
       If an old version is not deleted for a given replica , it is a duplicate




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