HBASE-26293 Use reservoir sampling when selecting bootstrap nodes

hbase-common/src/main/java/org/apache/hadoop/hbase/util/ReservoirSample.java

@@ -0,0 +1,72 @@
+/**
+ * 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.hadoop.hbase.util;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.stream.Stream;
+import org.apache.yetus.audience.InterfaceAudience;
+
+import org.apache.hbase.thirdparty.com.google.common.base.Preconditions;
+
+/**
+ * The simple version of reservoir sampling implementation. It is enough for the usage in HBase.
+ * <p/>
+ * See https://en.wikipedia.org/wiki/Reservoir_sampling.
+ */
+@InterfaceAudience.Private
+public class ReservoirSample<T> {
+
+  private final List<T> r;
+
+  private final int k;
+
+  private int n;
+
+  public ReservoirSample(int k) {
+    Preconditions.checkArgument(k > 0, "negative sampling number(%d) is not allowed");
+    r = new ArrayList<>(k);
+    this.k = k;
+  }
+
+  public void add(T t) {
+    if (n < k) {
+      r.add(t);
+    } else {
+      int j = ThreadLocalRandom.current().nextInt(n + 1);
+      if (j < k) {
+        r.set(j, t);
+      }
+    }
+    n++;
+  }
+
+  public void add(Iterator<T> iter) {
+    iter.forEachRemaining(this::add);
+  }
+
+  public void add(Stream<T> s) {
+    s.forEachOrdered(this::add);
+  }
+
+  public List<T> getSamplingResult() {
+    return r;
+  }
+}

hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestReservoirSample.java

@@ -0,0 +1,92 @@
+/**
+ * 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.hadoop.hbase.util;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+import java.util.stream.IntStream;
+import org.apache.hadoop.hbase.HBaseClassTestRule;
+import org.apache.hadoop.hbase.testclassification.MiscTests;
+import org.apache.hadoop.hbase.testclassification.SmallTests;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+
+@Category({ MiscTests.class, SmallTests.class })
+public class TestReservoirSample {
+
+  @ClassRule
+  public static final HBaseClassTestRule CLASS_RULE =
+    HBaseClassTestRule.forClass(TestReservoirSample.class);
+
+  @Test
+  public void test() {
+    int round = 100000;
+    int containsOne = 0;
+    for (int i = 0; i < round; i++) {
+      ReservoirSample<Integer> rs = new ReservoirSample<>(10);
+      for (int j = 0; j < 100; j++) {
+        rs.add(j);
+        if (j < 10) {
+          assertEquals(j + 1, rs.getSamplingResult().size());
+        } else {
+          assertEquals(10, rs.getSamplingResult().size());
+        }
+      }
+      if (rs.getSamplingResult().contains(1)) {
+        containsOne++;
+      }
+    }
+    // we assume a 5% error rate
+    assertTrue(containsOne > round / 10 * 0.95);
+    assertTrue(containsOne < round / 10 * 1.05);
+  }
+
+  @Test
+  public void testIterator() {
+    int round = 100000;
+    int containsOne = 0;
+    for (int i = 0; i < round; i++) {
+      ReservoirSample<Integer> rs = new ReservoirSample<>(10);
+      rs.add(IntStream.range(0, 100).mapToObj(Integer::valueOf).iterator());
+      if (rs.getSamplingResult().contains(1)) {
+        containsOne++;
+      }
+    }
+    // we assume a 5% error rate
+    assertTrue(containsOne > round / 10 * 0.95);
+    assertTrue(containsOne < round / 10 * 1.05);
+  }
+
+  @Test
+  public void testStream() {
+    int round = 100000;
+    int containsOne = 0;
+    for (int i = 0; i < round; i++) {
+      ReservoirSample<Integer> rs = new ReservoirSample<>(10);
+      rs.add(IntStream.range(0, 100).mapToObj(Integer::valueOf));
+      if (rs.getSamplingResult().contains(1)) {
+        containsOne++;
+      }
+    }
+    // we assume a 5% error rate
+    assertTrue(containsOne > round / 10 * 0.95);
+    assertTrue(containsOne < round / 10 * 1.05);
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/HBaseRpcServicesBase.java

@@ -22,11 +22,9 @@
 import java.lang.reflect.Method;
 import java.net.BindException;
 import java.net.InetSocketAddress;
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import java.util.Optional;
-import java.util.concurrent.ThreadLocalRandom;
 import org.apache.hadoop.conf.Configuration;
 import org.apache.hadoop.hbase.client.ConnectionUtils;
 import org.apache.hadoop.hbase.conf.ConfigurationObserver;
@@ -53,6 +51,7 @@
 import org.apache.hadoop.hbase.security.access.ZKPermissionWatcher;
 import org.apache.hadoop.hbase.util.DNS;
 import org.apache.hadoop.hbase.util.OOMEChecker;
+import org.apache.hadoop.hbase.util.ReservoirSample;
 import org.apache.hadoop.hbase.zookeeper.ZKWatcher;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.apache.zookeeper.KeeperException;
@@ -299,12 +298,13 @@ public GetMetaRegionLocationsResponse getMetaRegionLocations(RpcController contr
   @Override
   public final GetBootstrapNodesResponse getBootstrapNodes(RpcController controller,
     GetBootstrapNodesRequest request) throws ServiceException {
-    List<ServerName> bootstrapNodes = new ArrayList<>(server.getRegionServers());
-    Collections.shuffle(bootstrapNodes, ThreadLocalRandom.current());
     int maxNodeCount = server.getConfiguration().getInt(CLIENT_BOOTSTRAP_NODE_LIMIT,
       DEFAULT_CLIENT_BOOTSTRAP_NODE_LIMIT);
+    ReservoirSample<ServerName> sample = new ReservoirSample<>(maxNodeCount);
+    sample.add(server.getRegionServers());
+
     GetBootstrapNodesResponse.Builder builder = GetBootstrapNodesResponse.newBuilder();
-    bootstrapNodes.stream().limit(maxNodeCount).map(ProtobufUtil::toServerName)
+    sample.getSamplingResult().stream().map(ProtobufUtil::toServerName)
       .forEach(builder::addServerName);
     return builder.build();
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryEndpoint.java

@@ -17,7 +17,7 @@
  */
 package org.apache.hadoop.hbase.client;
 
-import java.util.Collection;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Optional;
 import org.apache.hadoop.hbase.HRegionLocation;
@@ -46,9 +46,9 @@ public interface ConnectionRegistryEndpoint {
   List<ServerName> getBackupMasters();
 
   /**
-   * Get all the region servers address.
+   * Get a iterator of the region servers which could be used as bootstrap nodes.
    */
-  Collection<ServerName> getRegionServers();
+  Iterator<ServerName> getRegionServers();
 
   /**
    * Get the location of meta regions.

hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java

@@ -3979,8 +3979,8 @@ public List<ServerName> getBackupMasters() {
   }
 
   @Override
-  public Collection<ServerName> getRegionServers() {
-    return regionServerTracker.getRegionServers();
+  public Iterator<ServerName> getRegionServers() {
+    return regionServerTracker.getRegionServers().iterator();
   }
 
   @Override

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java

@@ -34,6 +34,7 @@
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -3429,8 +3430,8 @@ public List<ServerName> getBackupMasters() {
   }
 
   @Override
-  public Collection<ServerName> getRegionServers() {
-    return regionServerAddressTracker.getRegionServers();
+  public Iterator<ServerName> getRegionServers() {
+    return regionServerAddressTracker.getRegionServers().iterator();
   }
 
   @Override