diff --git a/hbase-common/src/main/java/org/apache/hadoop/hbase/util/ReservoirSample.java b/hbase-common/src/main/java/org/apache/hadoop/hbase/util/ReservoirSample.java
new file mode 100644
index 000000000000..2cc502eb537b
--- /dev/null
+++ b/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.
+ *
+ * See https://en.wikipedia.org/wiki/Reservoir_sampling.
+ */
+@InterfaceAudience.Private
+public class ReservoirSample {
+
+ private final List 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 iter) {
+ iter.forEachRemaining(this::add);
+ }
+
+ public void add(Stream s) {
+ s.forEachOrdered(this::add);
+ }
+
+ public List getSamplingResult() {
+ return r;
+ }
+}
diff --git a/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestReservoirSample.java b/hbase-common/src/test/java/org/apache/hadoop/hbase/util/TestReservoirSample.java
new file mode 100644
index 000000000000..a4d23d47c47b
--- /dev/null
+++ b/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 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 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 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);
+ }
+}
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/HBaseRpcServicesBase.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/HBaseRpcServicesBase.java
index 4bd0b3304d40..21b2d757463e 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/HBaseRpcServicesBase.java
+++ b/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 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 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();
}
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryEndpoint.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryEndpoint.java
index 420c6d6b98e1..0a1557139b32 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryEndpoint.java
+++ b/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 getBackupMasters();
/**
- * Get all the region servers address.
+ * Get a iterator of the region servers which could be used as bootstrap nodes.
*/
- Collection getRegionServers();
+ Iterator getRegionServers();
/**
* Get the location of meta regions.
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java
index 9706149e82d5..45b980d86333 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java
+++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java
@@ -3979,8 +3979,8 @@ public List getBackupMasters() {
}
@Override
- public Collection getRegionServers() {
- return regionServerTracker.getRegionServers();
+ public Iterator getRegionServers() {
+ return regionServerTracker.getRegionServers().iterator();
}
@Override
diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
index cc22124dbeee..b45f33abeb4f 100644
--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/HRegionServer.java
+++ b/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 getBackupMasters() {
}
@Override
- public Collection getRegionServers() {
- return regionServerAddressTracker.getRegionServers();
+ public Iterator getRegionServers() {
+ return regionServerAddressTracker.getRegionServers().iterator();
}
@Override