[GitHub] [lucene-solr] noblepaul commented on a change in pull request #2148: SOLR-15052: Per-replica states for reducing overseer bottlenecks

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noblepaul commented on a change in pull request #2148:
URL: https://github.com/apache/lucene-solr/pull/2148#discussion_r552318967



##########
File path: solr/solrj/src/java/org/apache/solr/common/cloud/PerReplicaStates.java
##########
@@ -0,0 +1,600 @@
+/*
+ * 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.CreateMode;
+import org.apache.zookeeper.KeeperException;
+import org.apache.zookeeper.Op;
+import org.apache.zookeeper.data.ACL;
+import org.apache.zookeeper.data.Stat;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static java.util.Collections.singletonList;
+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 = ':';
+
+
+  @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;
+  }
+
+  /**
+   * This is a persist operation with retry if a write fails due to stale state
+   */
+  public static void persist(WriteOps ops, String znode, SolrZkClient zkClient) throws KeeperException, InterruptedException {
+    List<Operation> operations = ops.get();
+    for (int i = 0; i < 10; i++) {
+      try {
+        persist(operations, znode, zkClient);
+        return;
+      } catch (KeeperException.NodeExistsException | KeeperException.NoNodeException e) {
+        //state is stale
+        log.info("stale state for {}. retrying...", znode);
+        operations = ops.get(PerReplicaStates.fetch(znode, zkClient, null));
+      }
+    }
+  }
+
+  /**
+   * Persist a set of operations to Zookeeper
+   */
+  public static void persist(List<Operation> operations, String znode, SolrZkClient zkClient) throws KeeperException, InterruptedException {
+    if (operations == null || operations.isEmpty()) return;
+    log.debug("Per-replica state being persisted for :{}, ops: {}", znode, operations);
+
+    List<Op> ops = new ArrayList<>(operations.size());
+    for (Operation op : operations) {
+      //the state of the replica is being updated
+      String path = znode + "/" + op.state.asString;
+      List<ACL> acls = zkClient.getZkACLProvider().getACLsToAdd(path);
+      ops.add(op.typ == Operation.Type.ADD ?
+          Op.create(path, null, acls, CreateMode.PERSISTENT) :
+          Op.delete(path, -1));
+    }
+    try {
+      zkClient.multi(ops, true);
+      if (log.isDebugEnabled()) {
+        //nocommit
+        try {
+          Stat stat = zkClient.exists(znode, null, true);
+          log.debug("After update, cversion : {}", stat.getCversion());
+        } catch (Exception e) {
+        }
+
+      }
+    } catch (KeeperException e) {
+      log.error("multi op exception : " + e.getMessage() + zkClient.getChildren(znode, null, true));
+      throw e;

Review comment:
       does it add any value?




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