improve broker selector utils

pinot-clients/pinot-java-client/src/main/java/org/apache/pinot/client/BrokerCache.java

@@ -190,20 +190,14 @@ protected void updateBrokerData()
   }
 
   public String getBroker(String... tableNames) {
-    List<String> brokers = null;
     // If tableNames is not-null, filter out nulls
-    tableNames =
-        tableNames == null ? tableNames : Arrays.stream(tableNames).filter(Objects::nonNull).toArray(String[]::new);
-    if (!(tableNames == null || tableNames.length == 0)) {
-       // returning list of common brokers hosting all the tables.
-       brokers = BrokerSelectorUtils.getTablesCommonBrokers(Arrays.asList(tableNames),
-           _brokerData.getTableToBrokerMap());
+    tableNames = tableNames == null ? tableNames
+        : Arrays.stream(tableNames).filter(Objects::nonNull).toArray(String[]::new);
+    if (tableNames == null || tableNames.length == 0) {
+      List<String> brokers = _brokerData.getBrokers();
+      return brokers.get(ThreadLocalRandom.current().nextInt(brokers.size()));
     }
-
-    if (brokers == null || brokers.isEmpty()) {
-      brokers = _brokerData.getBrokers();
-    }
-    return brokers.get(ThreadLocalRandom.current().nextInt(brokers.size()));
+    return BrokerSelectorUtils.getRandomBroker(Arrays.asList(tableNames), _brokerData.getTableToBrokerMap());
   }
 
   public List<String> getBrokers() {

pinot-clients/pinot-java-client/src/main/java/org/apache/pinot/client/DynamicBrokerSelector.java

@@ -91,10 +91,10 @@ private void refresh() {
   public String selectBroker(String... tableNames) {
     if (!(tableNames == null || tableNames.length == 0 || tableNames[0] == null)) {
       // getting list of brokers hosting all the tables.
-      List<String> list = BrokerSelectorUtils.getTablesCommonBrokers(Arrays.asList(tableNames),
+      String randomBroker = BrokerSelectorUtils.getRandomBroker(Arrays.asList(tableNames),
           _tableToBrokerListMapRef.get());
-      if (list != null && !list.isEmpty()) {
-        return list.get(ThreadLocalRandom.current().nextInt(list.size()));
+      if (randomBroker != null) {
+        return randomBroker;
       }
     }
 

pinot-clients/pinot-java-client/src/main/java/org/apache/pinot/client/utils/BrokerSelectorUtils.java

@@ -19,9 +19,13 @@
 package org.apache.pinot.client.utils;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
+import java.util.Set;
+import java.util.concurrent.ThreadLocalRandom;
+import javax.annotation.Nullable;
 import org.apache.pinot.client.ExternalViewReader;
 
 
@@ -34,35 +38,52 @@ private BrokerSelectorUtils() {
    *
    * @param tableNames: List of table names.
    * @param brokerData: map holding data for table hosting on brokers.
-   * @return list of common brokers hosting all the tables.
+   * @return list of common brokers hosting all the tables or null if no common brokers found.
+   * @deprecated Use {@link #getTablesCommonBrokersSet(List, Map)} instead. It is more efficient and its semantics are
+   * clearer (ie it returns an empty set instead of null if no common brokers are found).
    */
-  public static List<String> getTablesCommonBrokers(List<String> tableNames, Map<String, List<String>> brokerData) {
-    List<List<String>> tablesBrokersList = new ArrayList<>();
-    for (String name: tableNames) {
-      String tableName = getTableNameWithoutSuffix(name);
-      int idx = tableName.indexOf('.');
-
-      if (brokerData.containsKey(tableName)) {
-        tablesBrokersList.add(brokerData.get(tableName));
-      } else if (idx > 0) {
-        // In case tableName is formatted as <db>.<table>
-        tableName = tableName.substring(idx + 1);
-        tablesBrokersList.add(brokerData.get(tableName));
-      }
+  @Nullable
+  @Deprecated
+  public static List<String> getTablesCommonBrokers(@Nullable List<String> tableNames,
+      Map<String, List<String>> brokerData) {
+    Set<String> tablesCommonBrokersSet = getTablesCommonBrokersSet(tableNames, brokerData);
+    if (tablesCommonBrokersSet == null || tablesCommonBrokersSet.isEmpty()) {
+      return null;
     }
+    return new ArrayList<>(tablesCommonBrokersSet);
+  }
 
-    // return null if tablesBrokersList is empty or contains null
-    if (tablesBrokersList.isEmpty()
-        || tablesBrokersList.stream().anyMatch(Objects::isNull)) {
+  /**
+   * Returns a random broker from the common brokers hosting all the tables.
+   */
+  @Nullable
+  public static String getRandomBroker(@Nullable List<String> tableNames, Map<String, List<String>> brokerData) {
+    Set<String> tablesCommonBrokersSet = getTablesCommonBrokersSet(tableNames, brokerData);
+    if (tablesCommonBrokersSet.isEmpty()) {
       return null;
     }
+    return tablesCommonBrokersSet.stream()
+        .skip(ThreadLocalRandom.current().nextInt(tablesCommonBrokersSet.size()))
+        .findFirst()
+        .orElseThrow(() -> new IllegalStateException("No broker found"));
+  }
 
-    // Make a copy of the brokersList of the first table. retainAll does inplace modifications.
-    // So lists from brokerData should not be used directly.
-    List<String> commonBrokers = new ArrayList<>(tablesBrokersList.get(0));
-    for (int i = 1; i < tablesBrokersList.size(); i++) {
-      commonBrokers.retainAll(tablesBrokersList.get(i));
+  /**
+   *
+   * @param tableNames: List of table names.
+   * @param brokerData: map holding data for table hosting on brokers.
+   * @return set of common brokers hosting all the tables
+   */
+  public static Set<String> getTablesCommonBrokersSet(
+      @Nullable List<String> tableNames, Map<String, List<String>> brokerData) {
+    if (tableNames == null || tableNames.isEmpty()) {
+      return Collections.emptySet();
+    }
+    HashSet<String> commonBrokers = getBrokers(tableNames.get(0), brokerData);
+    for (int i = 1; i < tableNames.size() && !commonBrokers.isEmpty(); i++) {
+      commonBrokers.retainAll(getBrokers(tableNames.get(i), brokerData));
     }
+
     return commonBrokers;
   }
 
@@ -71,4 +92,28 @@ private static String getTableNameWithoutSuffix(String tableName) {
         tableName.replace(ExternalViewReader.OFFLINE_SUFFIX, "").
             replace(ExternalViewReader.REALTIME_SUFFIX, "");
   }
+
+  /**
+   * Returns the brokers for the given table name.
+   *
+   * This means that an empty set is returned if there are no brokers for the given table name.
+   */
+  private static HashSet<String> getBrokers(String tableName, Map<String, List<String>> brokerData) {
+    String tableNameWithoutSuffix = getTableNameWithoutSuffix(tableName);
+    int idx = tableNameWithoutSuffix.indexOf('.');
+
+    List<String> brokers = brokerData.get(tableNameWithoutSuffix);
+    if (brokers != null) {
+      return new HashSet<>(brokers);
+    } else if (idx > 0) {
+      // TODO: This is probably unnecessary and even wrong. `brokerData` should include the fully qualified name.
+      // In case tableNameWithoutSuffix is formatted as <db>.<table> and not found in the fully qualified name
+      tableNameWithoutSuffix = tableNameWithoutSuffix.substring(idx + 1);
+      List<String> brokersWithoutDb = brokerData.get(tableNameWithoutSuffix);
+      if (brokersWithoutDb != null) {
+        return new HashSet<>(brokersWithoutDb);
+      }
+    }
+    return new HashSet<>();
+  }
 }

pinot-clients/pinot-java-client/src/test/java/org/apache/pinot/client/DynamicBrokerSelectorTest.java

@@ -152,4 +152,24 @@ public void testCloseZkClient() {
 
     Mockito.verify(_mockZkClient, times(1)).close();
   }
+
+  @Test
+  public void testSelectBrokerWithInvalidTable() {
+    Map<String, List<String>> tableToBrokerListMap = new HashMap<>();
+    tableToBrokerListMap.put("table1", Collections.singletonList("broker1"));
+    when(_mockExternalViewReader.getTableToBrokersMap()).thenReturn(tableToBrokerListMap);
+    _dynamicBrokerSelectorUnderTest.handleDataChange("dataPath", "data");
+    String result = _dynamicBrokerSelectorUnderTest.selectBroker("invalidTable");
+    assertEquals(result, "broker1");
+  }
+
+  @Test
+  public void testSelectBrokerWithTwoTablesOneInvalid() {
+    Map<String, List<String>> tableToBrokerListMap = new HashMap<>();
+    tableToBrokerListMap.put("table1", Collections.singletonList("broker1"));
+    when(_mockExternalViewReader.getTableToBrokersMap()).thenReturn(tableToBrokerListMap);
+    _dynamicBrokerSelectorUnderTest.handleDataChange("dataPath", "data");
+    String result = _dynamicBrokerSelectorUnderTest.selectBroker("table1", "invalidTable");
+    assertEquals(result, "broker1");
+  }
 }

pinot-clients/pinot-java-client/src/test/java/org/apache/pinot/client/utils/BrokerSelectorUtilsTest.java

@@ -0,0 +1,121 @@
+/**
+ * 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.pinot.client.utils;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Set;
+import org.testng.Assert;
+import org.testng.annotations.AfterMethod;
+import org.testng.annotations.Test;
+
+
+public class BrokerSelectorUtilsTest {
+
+  HashMap<String, List<String>> _brokerData = new HashMap<>();
+  @Test
+  public void getTablesCommonBrokersSetNullTables() {
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(null, _brokerData);
+    Assert.assertEquals(tableSet, Set.of());
+  }
+
+  @Test
+  public void getTablesCommonBrokersListNullTables() {
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(null, _brokerData);
+    Assert.assertNull(tableList);
+  }
+
+  @Test
+  public void getTablesCommonBrokersSetEmptyTables() {
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(List.of(), _brokerData);
+    Assert.assertEquals(tableSet, Set.of());
+  }
+
+  @Test
+  public void getTablesCommonBrokersListEmptyTables() {
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(List.of(), _brokerData);
+    Assert.assertNull(tableList);
+  }
+
+  @Test
+  public void getTablesCommonBrokersSetNotExistentTable() {
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(List.of("notExistent"), _brokerData);
+    Assert.assertEquals(tableSet, Set.of());
+  }
+
+  @Test
+  public void getTablesCommonBrokersListNotExistentTable() {
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(List.of("notExistent"), _brokerData);
+    Assert.assertNull(tableList);
+  }
+
+  @Test
+  public void getTablesCommonBrokersSetOneTable() {
+    _brokerData.put("table1", List.of("broker1"));
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(List.of("table1"), _brokerData);
+    Assert.assertEquals(tableSet, Set.of("broker1"));
+  }
+
+  @Test
+  public void getTablesCommonBrokersListOneTable() {
+    _brokerData.put("table1", List.of("broker1"));
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(List.of("table1"), _brokerData);
+    Assert.assertNotNull(tableList);
+    Assert.assertEquals(tableList, List.of("broker1"));
+  }
+
+  @Test
+  public void getTablesCommonBrokersSetTwoTables() {
+    _brokerData.put("table1", List.of("broker1"));
+    _brokerData.put("table2", List.of("broker1"));
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(List.of("table1", "table2"), _brokerData);
+    Assert.assertNotNull(tableSet);
+    Assert.assertEquals(tableSet, Set.of("broker1"));
+  }
+
+  @Test
+  public void getTablesCommonBrokersListTwoTables() {
+    _brokerData.put("table1", List.of("broker1"));
+    _brokerData.put("table2", List.of("broker1"));
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(List.of("table1", "table2"), _brokerData);
+    Assert.assertNotNull(tableList);
+    Assert.assertEquals(tableList, List.of("broker1"));
+  }
+
+  @Test
+  public void getTablesCommonBrokersSetTwoTablesDifferentBrokers() {
+    _brokerData.put("table1", List.of("broker1"));
+    _brokerData.put("table2", List.of("broker2"));
+    Set<String> tableSet = BrokerSelectorUtils.getTablesCommonBrokersSet(List.of("table1", "table2"), _brokerData);
+    Assert.assertEquals(tableSet, Set.of());
+  }
+
+  @Test
+  public void getTablesCommonBrokersListTwoTablesDifferentBrokers() {
+    _brokerData.put("table1", List.of("broker1"));
+    _brokerData.put("table2", List.of("broker2"));
+    List<String> tableList = BrokerSelectorUtils.getTablesCommonBrokers(List.of("table1", "table2"), _brokerData);
+    Assert.assertNull(tableList);
+  }
+
+  @AfterMethod
+  public void tearDown() {
+    _brokerData.clear();
+  }
+}