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Posted to jira@kafka.apache.org by GitBox <gi...@apache.org> on 2021/03/08 19:10:11 UTC

[GitHub] [kafka] chia7712 commented on a change in pull request #10275: KAFKA-12434; Admin support for `DescribeProducers` API

chia7712 commented on a change in pull request #10275:
URL: https://github.com/apache/kafka/pull/10275#discussion_r589631318



##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/DescribeProducersResult.java
##########
@@ -0,0 +1,76 @@
+/*
+ * 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.kafka.clients.admin;
+
+import org.apache.kafka.common.KafkaException;
+import org.apache.kafka.common.KafkaFuture;
+import org.apache.kafka.common.TopicPartition;
+import org.apache.kafka.common.annotation.InterfaceStability;
+import org.apache.kafka.common.internals.KafkaFutureImpl;
+
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ExecutionException;
+
+@InterfaceStability.Evolving
+public class DescribeProducersResult {
+
+    private final Map<TopicPartition, KafkaFutureImpl<PartitionProducerState>> futures;
+
+    DescribeProducersResult(Map<TopicPartition, KafkaFutureImpl<PartitionProducerState>> futures) {
+        this.futures = futures;
+    }
+
+    public KafkaFuture<PartitionProducerState> partitionResult(final TopicPartition partition) {
+        KafkaFuture<PartitionProducerState> future = futures.get(partition);
+        if (future == null) {
+            throw new IllegalArgumentException("Topic partition " + partition +
+                " was not included in the request");
+        }
+        return future;
+    }
+
+    public KafkaFuture<Map<TopicPartition, PartitionProducerState>> all() {
+        return KafkaFuture.allOf(futures.values().toArray(new KafkaFuture[0]))
+            .thenApply(nil -> {
+                Map<TopicPartition, PartitionProducerState> results = new HashMap<>(futures.size());
+                for (Map.Entry<TopicPartition, KafkaFutureImpl<PartitionProducerState>> entry : futures.entrySet()) {
+                    try {
+                        results.put(entry.getKey(), entry.getValue().get());
+                    } catch (InterruptedException | ExecutionException e) {
+                        // This should be unreachable, because allOf ensured that all the futures completed successfully.
+                        throw new KafkaException(e);
+                    }
+                }
+                return results;
+            });
+    }
+
+    public static class PartitionProducerState {
+        private final List<ProducerState> activeProducers;
+
+        public PartitionProducerState(List<ProducerState> activeProducers) {

Review comment:
       Could we change the modifier from public to package-private? Exposing this constructor to users is useless.

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/DescribeProducersOptions.java
##########
@@ -0,0 +1,63 @@
+/*
+ * 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.kafka.clients.admin;
+
+import org.apache.kafka.common.annotation.InterfaceStability;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.OptionalInt;
+
+/**
+ * Options for {@link Admin#describeProducers(Collection)}.
+ *
+ * The API of this class is evolving, see {@link Admin} for details.
+ */
+@InterfaceStability.Evolving
+public class DescribeProducersOptions extends AbstractOptions<DescribeProducersOptions> {

Review comment:
       Could we make it override `timeoutMs` in order to write following code.
   ```java
   new DescribeProducersOptions()
     .timeoutMs(11)
     .setBrokerId(1)
   ```

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/DescribeProducersOptions.java
##########
@@ -0,0 +1,63 @@
+/*
+ * 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.kafka.clients.admin;
+
+import org.apache.kafka.common.annotation.InterfaceStability;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.OptionalInt;
+
+/**
+ * Options for {@link Admin#describeProducers(Collection)}.
+ *
+ * The API of this class is evolving, see {@link Admin} for details.
+ */
+@InterfaceStability.Evolving
+public class DescribeProducersOptions extends AbstractOptions<DescribeProducersOptions> {
+    private OptionalInt brokerId = OptionalInt.empty();
+
+    public DescribeProducersOptions setBrokerId(int brokerId) {

Review comment:
       Other options classes does not call it `setXXX`. Maybe we should following consistent naming?

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/DescribeProducersOptions.java
##########
@@ -0,0 +1,63 @@
+/*
+ * 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.kafka.clients.admin;
+
+import org.apache.kafka.common.annotation.InterfaceStability;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.OptionalInt;
+
+/**
+ * Options for {@link Admin#describeProducers(Collection)}.
+ *
+ * The API of this class is evolving, see {@link Admin} for details.
+ */
+@InterfaceStability.Evolving
+public class DescribeProducersOptions extends AbstractOptions<DescribeProducersOptions> {
+    private OptionalInt brokerId = OptionalInt.empty();
+
+    public DescribeProducersOptions setBrokerId(int brokerId) {
+        this.brokerId = OptionalInt.of(brokerId);
+        return this;
+    }
+
+    public OptionalInt brokerId() {
+        return brokerId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        DescribeProducersOptions that = (DescribeProducersOptions) o;
+        return Objects.equals(brokerId, that.brokerId);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(brokerId);

Review comment:
       include `timeoutMs`?

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiDriver.java
##########
@@ -0,0 +1,464 @@
+/*
+ * 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.kafka.clients.admin.internals;
+
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.DynamicKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.KeyMappings;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.StaticKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiLookupStrategy.RequestScope;
+import org.apache.kafka.common.errors.DisconnectException;
+import org.apache.kafka.common.internals.KafkaFutureImpl;
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.function.BiFunction;
+
+/**
+ * The `KafkaAdminClient`'s internal `Call` primitive is not a good fit for multi-stage
+ * request workflows such as we see with the group coordinator APIs or any request which
+ * needs to be sent to a partition leader. Typically these APIs have two concrete stages:
+ *
+ * 1. Lookup: Find the broker that can fulfill the request (e.g. partition leader or group
+ *            coordinator)
+ * 2. Fulfillment: Send the request to the broker found in the first step
+ *
+ * This is complicated by the fact that `Admin` APIs are typically batched, which
+ * means the Lookup stage may result in a set of brokers. For example, take a `ListOffsets`
+ * request for a set of topic partitions. In the Lookup stage, we will find the partition
+ * leaders for this set of partitions; in the Fulfillment stage, we will group together
+ * partition according to the IDs of the discovered leaders.
+ *
+ * Additionally, the flow between these two stages is bi-directional. We may find after
+ * sending a `ListOffsets` request to an expected leader that there was a leader change.
+ * This would result in a topic partition being sent back to the Lookup stage.
+ *
+ * Managing this complexity by chaining together `Call` implementations is challenging
+ * and messy, so instead we use this class to do the bookkeeping. It handles both the
+ * batching aspect as well as the transitions between the Lookup and Fulfillment stages.
+ *
+ * Note that the interpretation of the `retries` configuration becomes ambiguous
+ * for this kind of pipeline. We could treat it as an overall limit on the number
+ * of requests that can be sent, but that is not very useful because each pipeline
+ * has a minimum number of requests that need to be sent in order to satisfy the request.
+ * Instead, we treat this number of retries independently at each stage so that each
+ * stage has at least one opportunity to complete. So if a user sets `retries=1`, then
+ * the full pipeline can still complete as long as there are no request failures.
+ *
+ * @param <K> The key type, which is also the granularity of the request routing (e.g.
+ *            this could be `TopicPartition` in the case of requests intended for a partition
+ *            leader or the `GroupId` in the case of consumer group requests intended for
+ *            the group coordinator)
+ * @param <V> The fulfillment type for each key (e.g. this could be consumer group state
+ *            when the key type is a consumer `GroupId`)
+ */
+public class AdminApiDriver<K, V> {
+    private final Logger log;
+    private final long retryBackoffMs;
+    private final long deadlineMs;
+    private final AdminApiHandler<K, V> handler;
+    private final Optional<StaticKeyMapping<K>> staticMapping;
+    private final Optional<DynamicKeyMapping<K>> dynamicMapping;
+    private final Map<K, KafkaFutureImpl<V>> futures;
+
+    private final BiMultimap<RequestScope, K> lookupMap = new BiMultimap<>();
+    private final BiMultimap<BrokerScope, K> fulfillmentMap = new BiMultimap<>();
+    private final Map<RequestScope, RequestState> requestStates = new HashMap<>();
+
+
+    public AdminApiDriver(
+        AdminApiHandler<K, V> handler,
+        long deadlineMs,
+        long retryBackoffMs,
+        LogContext logContext
+    ) {
+        this.handler = handler;
+        this.deadlineMs = deadlineMs;
+        this.retryBackoffMs = retryBackoffMs;
+        this.log = logContext.logger(AdminApiDriver.class);
+        this.futures = new HashMap<>();
+
+        KeyMappings<K> result = handler.initializeKeys();
+        this.dynamicMapping = result.dynamicMapping;
+        this.staticMapping = result.staticMapping;
+
+        initializeKeys();
+    }
+
+    private void initializeKeys() {
+        staticMapping.ifPresent(mapping -> {
+            for (Map.Entry<K, Integer> staticMapping : mapping.keys.entrySet()) {
+                K key = staticMapping.getKey();
+                Integer brokerId = staticMapping.getValue();
+                futures.put(key, new KafkaFutureImpl<>());
+                map(key, brokerId);
+            }
+        });
+
+        dynamicMapping.ifPresent(mapping -> {
+            for (K key : mapping.keys) {
+                futures.put(key, new KafkaFutureImpl<>());
+                lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+            }
+        });
+    }
+
+    /**
+     * Associate a key with a brokerId. This is called after a response in the Lookup
+     * stage reveals the mapping (e.g. when the `FindCoordinator` tells us the the
+     * group coordinator for a specific consumer group).
+     */
+    private void map(K key, Integer brokerId) {
+        lookupMap.remove(key);
+        fulfillmentMap.put(new BrokerScope(brokerId), key);
+
+        // To allow for derived keys, we create futures dynamically if they
+        // do not already exist in the future map
+        futures.computeIfAbsent(key, k -> new KafkaFutureImpl<>());
+    }
+
+    /**
+     * Disassociate a key from the currently mapped brokerId. This will send the key
+     * back to the Lookup stage, which will allow us to attempt lookup again.
+     */
+    private void unmap(K key) {
+        DynamicKeyMapping<K> mapping = dynamicMapping.orElseThrow(() ->
+            new IllegalStateException("Attempt to unmap key " + key + " which is not dynamically mapped")
+        );
+        fulfillmentMap.remove(key);
+        lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+    }
+
+    private void clear(K key) {
+        lookupMap.remove(key);
+        fulfillmentMap.remove(key);
+    }
+
+    OptionalInt keyToBrokerId(K key) {

Review comment:
       It seems `keyToBrokerId` (and `getKey`) are used by testing only. Is it worthwhile to keep a `reverseMap` in production code for testing? 

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiDriver.java
##########
@@ -0,0 +1,464 @@
+/*
+ * 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.kafka.clients.admin.internals;
+
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.DynamicKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.KeyMappings;
+import org.apache.kafka.clients.admin.internals.AdminApiHandler.StaticKeyMapping;
+import org.apache.kafka.clients.admin.internals.AdminApiLookupStrategy.RequestScope;
+import org.apache.kafka.common.errors.DisconnectException;
+import org.apache.kafka.common.internals.KafkaFutureImpl;
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+import org.apache.kafka.common.utils.LogContext;
+import org.slf4j.Logger;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Optional;
+import java.util.OptionalInt;
+import java.util.Set;
+import java.util.function.BiFunction;
+
+/**
+ * The `KafkaAdminClient`'s internal `Call` primitive is not a good fit for multi-stage
+ * request workflows such as we see with the group coordinator APIs or any request which
+ * needs to be sent to a partition leader. Typically these APIs have two concrete stages:
+ *
+ * 1. Lookup: Find the broker that can fulfill the request (e.g. partition leader or group
+ *            coordinator)
+ * 2. Fulfillment: Send the request to the broker found in the first step
+ *
+ * This is complicated by the fact that `Admin` APIs are typically batched, which
+ * means the Lookup stage may result in a set of brokers. For example, take a `ListOffsets`
+ * request for a set of topic partitions. In the Lookup stage, we will find the partition
+ * leaders for this set of partitions; in the Fulfillment stage, we will group together
+ * partition according to the IDs of the discovered leaders.
+ *
+ * Additionally, the flow between these two stages is bi-directional. We may find after
+ * sending a `ListOffsets` request to an expected leader that there was a leader change.
+ * This would result in a topic partition being sent back to the Lookup stage.
+ *
+ * Managing this complexity by chaining together `Call` implementations is challenging
+ * and messy, so instead we use this class to do the bookkeeping. It handles both the
+ * batching aspect as well as the transitions between the Lookup and Fulfillment stages.
+ *
+ * Note that the interpretation of the `retries` configuration becomes ambiguous
+ * for this kind of pipeline. We could treat it as an overall limit on the number
+ * of requests that can be sent, but that is not very useful because each pipeline
+ * has a minimum number of requests that need to be sent in order to satisfy the request.
+ * Instead, we treat this number of retries independently at each stage so that each
+ * stage has at least one opportunity to complete. So if a user sets `retries=1`, then
+ * the full pipeline can still complete as long as there are no request failures.
+ *
+ * @param <K> The key type, which is also the granularity of the request routing (e.g.
+ *            this could be `TopicPartition` in the case of requests intended for a partition
+ *            leader or the `GroupId` in the case of consumer group requests intended for
+ *            the group coordinator)
+ * @param <V> The fulfillment type for each key (e.g. this could be consumer group state
+ *            when the key type is a consumer `GroupId`)
+ */
+public class AdminApiDriver<K, V> {
+    private final Logger log;
+    private final long retryBackoffMs;
+    private final long deadlineMs;
+    private final AdminApiHandler<K, V> handler;
+    private final Optional<StaticKeyMapping<K>> staticMapping;
+    private final Optional<DynamicKeyMapping<K>> dynamicMapping;
+    private final Map<K, KafkaFutureImpl<V>> futures;
+
+    private final BiMultimap<RequestScope, K> lookupMap = new BiMultimap<>();
+    private final BiMultimap<BrokerScope, K> fulfillmentMap = new BiMultimap<>();
+    private final Map<RequestScope, RequestState> requestStates = new HashMap<>();
+
+
+    public AdminApiDriver(
+        AdminApiHandler<K, V> handler,
+        long deadlineMs,
+        long retryBackoffMs,
+        LogContext logContext
+    ) {
+        this.handler = handler;
+        this.deadlineMs = deadlineMs;
+        this.retryBackoffMs = retryBackoffMs;
+        this.log = logContext.logger(AdminApiDriver.class);
+        this.futures = new HashMap<>();
+
+        KeyMappings<K> result = handler.initializeKeys();
+        this.dynamicMapping = result.dynamicMapping;
+        this.staticMapping = result.staticMapping;
+
+        initializeKeys();
+    }
+
+    private void initializeKeys() {
+        staticMapping.ifPresent(mapping -> {
+            for (Map.Entry<K, Integer> staticMapping : mapping.keys.entrySet()) {
+                K key = staticMapping.getKey();
+                Integer brokerId = staticMapping.getValue();
+                futures.put(key, new KafkaFutureImpl<>());
+                map(key, brokerId);
+            }
+        });
+
+        dynamicMapping.ifPresent(mapping -> {
+            for (K key : mapping.keys) {
+                futures.put(key, new KafkaFutureImpl<>());
+                lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+            }
+        });
+    }
+
+    /**
+     * Associate a key with a brokerId. This is called after a response in the Lookup
+     * stage reveals the mapping (e.g. when the `FindCoordinator` tells us the the
+     * group coordinator for a specific consumer group).
+     */
+    private void map(K key, Integer brokerId) {
+        lookupMap.remove(key);
+        fulfillmentMap.put(new BrokerScope(brokerId), key);
+
+        // To allow for derived keys, we create futures dynamically if they
+        // do not already exist in the future map
+        futures.computeIfAbsent(key, k -> new KafkaFutureImpl<>());
+    }
+
+    /**
+     * Disassociate a key from the currently mapped brokerId. This will send the key
+     * back to the Lookup stage, which will allow us to attempt lookup again.
+     */
+    private void unmap(K key) {
+        DynamicKeyMapping<K> mapping = dynamicMapping.orElseThrow(() ->
+            new IllegalStateException("Attempt to unmap key " + key + " which is not dynamically mapped")
+        );
+        fulfillmentMap.remove(key);
+        lookupMap.put(mapping.lookupStrategy.lookupScope(key), key);
+    }
+
+    private void clear(K key) {
+        lookupMap.remove(key);
+        fulfillmentMap.remove(key);
+    }
+
+    OptionalInt keyToBrokerId(K key) {
+        Optional<BrokerScope> scope = fulfillmentMap.getKey(key);
+        if (scope.isPresent()) {
+            return OptionalInt.of(scope.get().destinationBrokerId);
+        } else {
+            return OptionalInt.empty();
+        }
+    }
+
+    /**
+     * Complete the future associated with the given key exceptionally. After is called,
+     * the key will be taken out of both the Lookup and Fulfillment stages so that request
+     * are not retried.
+     */
+    private void completeExceptionally(K key, Throwable t) {
+        KafkaFutureImpl<V> future = futures.get(key);
+        if (future == null) {
+            log.warn("Attempt to complete future for {}, which was not requested", key);
+        } else {
+            clear(key);
+            future.completeExceptionally(t);
+        }
+    }
+
+    /**
+     * Complete the future associated with the given key. After is called, the key will
+     * be taken out of both the Lookup and Fulfillment stages so that request are not retried.
+     */
+    private void complete(K key, V value) {
+        KafkaFutureImpl<V> future = futures.get(key);
+        if (future == null) {
+            log.warn("Attempt to complete future for {}, which was not requested", key);
+        } else {
+            clear(key);
+            future.complete(value);
+        }
+    }
+
+    /**
+     * Check whether any requests need to be sent. This should be called immediately
+     * after the driver is constructed and then again after each request returns
+     * (i.e. after {@link #onFailure(long, RequestSpec, Throwable)} or
+     * {@link #onResponse(long, RequestSpec, AbstractResponse)}).
+     *
+     * @return A list of requests that need to be sent
+     */
+    public List<RequestSpec<K>> poll() {
+        List<RequestSpec<K>> requests = new ArrayList<>();
+        collectLookupRequests(requests);
+        collectFulfillmentRequests(requests);
+        return requests;
+    }
+
+    /**
+     * Get a map of the futures that are awaiting completion.
+     */
+    public Map<K, KafkaFutureImpl<V>> futures() {
+        return futures;
+    }
+
+    /**
+     * Callback that is invoked when a `Call` returns a response successfully.
+     */
+    public void onResponse(
+        long currentTimeMs,
+        RequestSpec<K> spec,
+        AbstractResponse response
+    ) {
+        clearInflightRequest(currentTimeMs, spec);
+        if (spec.scope instanceof AdminApiDriver.BrokerScope) {
+            int brokerId = ((BrokerScope) spec.scope).destinationBrokerId;
+            AdminApiHandler.ApiResult<K, V> result = handler.handleResponse(
+                brokerId,
+                spec.keys,
+                response
+            );
+            result.completedKeys.forEach(this::complete);
+            result.failedKeys.forEach(this::completeExceptionally);
+            result.unmappedKeys.forEach(this::unmap);
+        } else {
+            DynamicKeyMapping<K> mapping = dynamicMapping.orElseThrow(() ->
+                new IllegalStateException("Received response for unexpected dynamic lookup scope " + spec.scope)
+            );
+
+            AdminApiLookupStrategy.LookupResult<K> result = mapping.lookupStrategy.handleResponse(
+                spec.keys,
+                response
+            );
+            result.failedKeys.forEach(this::completeExceptionally);
+            result.mappedKeys.forEach(this::map);
+        }
+    }
+
+    /**
+     * Callback that is invoked when a `Call` is failed.
+     */
+    public void onFailure(
+        long currentTimeMs,
+        RequestSpec<K> spec,
+        Throwable t
+    ) {
+        clearInflightRequest(currentTimeMs, spec);
+        if (t instanceof DisconnectException) {
+            log.debug("Node disconnected before response could be received for request {}. " +
+                "Will attempt retry", spec.request);
+            dynamicMapping.ifPresent(mapping -> {
+                if (mapping.keys.containsAll(spec.keys)) {
+                    spec.keys.forEach(this::unmap);
+                }
+            });
+        } else {
+            spec.keys.forEach(key -> completeExceptionally(key, t));
+        }
+    }
+
+    private void clearInflightRequest(long currentTimeMs, RequestSpec<K> spec) {
+        RequestState requestState = requestStates.get(spec.scope);
+        if (requestState != null) {
+            requestState.clearInflight(currentTimeMs);
+        }
+    }
+
+    private <T extends RequestScope> void collectRequests(
+        List<RequestSpec<K>> requests,
+        BiMultimap<T, K> multimap,
+        BiFunction<Set<K>, T, AbstractRequest.Builder<?>> buildRequest
+    ) {
+        for (Map.Entry<T, Set<K>> entry : multimap.entrySet()) {
+            T scope = entry.getKey();
+
+            Set<K> keys = entry.getValue();
+            if (keys.isEmpty()) {
+                continue;
+            }
+
+            RequestState requestState = requestStates.computeIfAbsent(scope, c -> new RequestState());
+            if (requestState.hasInflight()) {
+                continue;
+            }
+
+            AbstractRequest.Builder<?> request = buildRequest.apply(keys, scope);
+            RequestSpec<K> spec = new RequestSpec<>(
+                handler.apiName() + "(api=" + request.apiKey() + ")",
+                scope,
+                new HashSet<>(keys), // copy to avoid exposing mutable state
+                request,
+                requestState.nextAllowedRetryMs,
+                deadlineMs,
+                requestState.tries
+            );
+
+            requestState.setInflight(spec);
+            requests.add(spec);
+        }
+    }
+
+    private void collectLookupRequests(List<RequestSpec<K>> requests) {
+        dynamicMapping.ifPresent(mapping -> {
+            collectRequests(
+                requests,
+                lookupMap,
+                (keys, scope) -> mapping.lookupStrategy.buildRequest(keys)
+            );
+        });
+    }
+
+    private void collectFulfillmentRequests(List<RequestSpec<K>> requests) {
+        collectRequests(
+            requests,
+            fulfillmentMap,
+            (keys, scope) -> handler.buildRequest(scope.destinationBrokerId, keys)
+        );
+    }
+
+    /**
+     * This is a helper class which helps us to map requests that need to be sent
+     * to the internal `Call` implementation that is used internally in
+     * {@link org.apache.kafka.clients.admin.KafkaAdminClient}.
+     */
+    public static class RequestSpec<K> {
+        public final String name;
+        public final RequestScope scope;
+        public final Set<K> keys;
+        public final AbstractRequest.Builder<?> request;
+        public final long nextAllowedTryMs;
+        public final long deadlineMs;
+        public final int tries;
+
+        public RequestSpec(
+            String name,
+            RequestScope scope,
+            Set<K> keys,
+            AbstractRequest.Builder<?> request,
+            long nextAllowedTryMs,
+            long deadlineMs,
+            int tries
+        ) {
+            this.name = name;
+            this.scope = scope;
+            this.keys = keys;
+            this.request = request;
+            this.nextAllowedTryMs = nextAllowedTryMs;
+            this.deadlineMs = deadlineMs;
+            this.tries = tries;
+        }
+    }
+
+    /**
+     * Helper class used to track the request state within each request scope.
+     * This class enforces a maximum number of inflight request and keeps track
+     * of backoff/retry state.
+     */
+    private class RequestState {
+        private Optional<RequestSpec<K>> inflightRequest = Optional.empty();
+        private int tries = 0;
+        private long nextAllowedRetryMs = 0;
+
+        boolean hasInflight() {
+            return inflightRequest.isPresent();
+        }
+
+        public void clearInflight(long currentTimeMs) {
+            this.inflightRequest = Optional.empty();
+            this.nextAllowedRetryMs = currentTimeMs + retryBackoffMs;
+        }
+
+        public void setInflight(RequestSpec<K> spec) {
+            this.inflightRequest = Optional.of(spec);
+            this.tries++;
+        }
+    }
+
+    /**
+     * Completion of the Lookup stage results in a destination broker to send the
+     * fulfillment request to. Each destination broker in the Fulfillment stage
+     * gets its own request scope.
+     */
+    private static class BrokerScope implements RequestScope {
+        public final int destinationBrokerId;
+
+        private BrokerScope(int destinationBrokerId) {
+            this.destinationBrokerId = destinationBrokerId;
+        }
+
+        @Override
+        public OptionalInt destinationBrokerId() {
+            return OptionalInt.of(destinationBrokerId);
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            BrokerScope that = (BrokerScope) o;
+            return destinationBrokerId == that.destinationBrokerId;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(destinationBrokerId);
+        }
+    }
+
+    /**
+     * Helper class which maintains a bi-directional mapping from a key to a set of values.
+     * Each value can map to one and only one key, but many values can be associated with
+     * a single key.
+     *
+     * @param <K> The key type
+     * @param <V> The value type
+     */
+    private static class BiMultimap<K, V> {
+        private final Map<V, K> reverseMap = new HashMap<>();
+        private final Map<K, Set<V>> map = new HashMap<>();
+
+        void put(K key, V value) {
+            remove(value);
+            reverseMap.put(value, key);
+            map.computeIfAbsent(key, k -> new HashSet<>()).add(value);
+        }
+
+        void remove(V value) {
+            K key = reverseMap.remove(value);
+            if (key != null) {
+                Set<V> set = map.get(key);
+                if (set != null) {
+                    set.remove(value);
+                    if (set.isEmpty()) {
+                        map.remove(key);
+                    }
+                }
+            }
+        }
+
+        Optional<K> getKey(V value) {
+            return Optional.ofNullable(reverseMap.get(value));

Review comment:
       Is this method safe? If there are same values, it would return unrelated key.

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiHandler.java
##########
@@ -0,0 +1,127 @@
+/*
+ * 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.kafka.clients.admin.internals;
+
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+public interface AdminApiHandler<K, V> {
+
+    /**
+     * Get a user-friendly name for the API this handler is implementing.
+     */
+    String apiName();
+
+    /**
+     * Initialize the set of keys required to handle this API and how the driver
+     * should map them to the broker that will handle the request for these keys.
+     *
+     * Two mapping types are supported:
+     *
+     * - Static mapping: when the brokerId is known ahead of time
+     * - Dynamic mapping: when the brokerId must be discovered dynamically
+     *
+     * @return the key mappings
+     */
+    KeyMappings<K> initializeKeys();
+
+    /**
+     * Build the fulfillment request. The set of keys are derived during the Lookup stage
+     * as the set of keys which all map to the same destination broker.
+     *
+     * @param brokerId the target brokerId for the request
+     * @param keys the set of keys that should be handled by this request
+     *
+     * @return a builder for the request containing the given keys
+     */
+    AbstractRequest.Builder<?> buildRequest(Integer brokerId, Set<K> keys);
+
+    /**
+     * Callback that is invoked when a Fulfillment request returns successfully.
+     * The handler should parse the response, check for errors, and return a
+     * result which indicates which keys (if any) have either been completed or
+     * failed with an unrecoverable error.
+     *
+     * It is also possible that the response indicates an incorrect target brokerId
+     * (e.g. in the case of a NotLeader error when the request is bound for a partition
+     * leader). In this case the key will be "unmapped" from the target brokerId
+     * and lookup will be retried.
+     *
+     * Note that keys which received a retriable error should be left out of the
+     * result. They will be retried automatically.
+     *
+     * @param brokerId the brokerId that the associated request was sent to
+     * @param keys the set of keys from the associated request
+     * @param response the response received from the broker
+     *
+     * @return result indicating key complation, failure, and unmapping
+     */
+    ApiResult<K, V> handleResponse(Integer brokerId, Set<K> keys, AbstractResponse response);
+
+    class KeyMappings<K> {
+        public final Optional<StaticKeyMapping<K>> staticMapping;
+        public final Optional<DynamicKeyMapping<K>> dynamicMapping;
+
+        public KeyMappings(
+            Optional<StaticKeyMapping<K>> staticMapping,
+            Optional<DynamicKeyMapping<K>> dynamicMapping
+        ) {
+            this.staticMapping = staticMapping;
+            this.dynamicMapping = dynamicMapping;
+        }
+    }
+
+    class StaticKeyMapping<K> {
+        public final Map<K, Integer> keys;
+
+        public StaticKeyMapping(Map<K, Integer> keys) {
+            this.keys = keys;

Review comment:
       Why this field is not wrapped to unmodified stuff?

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiLookupStrategy.java
##########
@@ -0,0 +1,94 @@
+/*
+ * 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.kafka.clients.admin.internals;
+
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+
+import java.util.Collections;
+import java.util.Map;
+import java.util.OptionalInt;
+import java.util.Set;
+
+public interface AdminApiLookupStrategy<T> {
+
+    /**
+     * Define the scope of a given key for lookup. Key lookups are complicated
+     * by the need to accommodate different batching mechanics. For example,
+     * a `Metadata` request supports arbitrary batching of topic partitions in
+     * order to discover partitions leaders. This can be supported by returning
+     * a single scope object for all keys.
+     *
+     * On the other hand, `FindCoordinator` request only supports lookup of a
+     * single key. This can be supported by returning a different scope object
+     * for each lookup key.
+     *
+     * @param key the lookup key
+     *
+     * @return request scope indicating how lookup requests can be batched together
+     */
+    RequestScope lookupScope(T key);
+
+    /**
+     * Build the lookup request for a set of keys. The grouping of the keys is controlled
+     * through {@link #lookupScope(Object)}. In other words, each set of keys that map
+     * to the same request scope object will be sent to this method.
+     *
+     * @param keys the set of keys that require lookup
+     *
+     * @return a builder for the lookup request
+     */
+    AbstractRequest.Builder<?> buildRequest(Set<T> keys);
+
+    /**
+     * Callback that is invoked when a lookup request returns successfully. The handler
+     * should parse the response, check for errors, and return a result indicating
+     * which keys were mapped to a brokerId successfully and which keys received
+     * a fatal error (e.g. a topic authorization failure).
+     *
+     * Note that keys which receive a retriable error should be left out of the
+     * result. They will be retried automatically. For example, if the response of
+     * `FindCoordinator` request indicates an unavailable coordinator, then the key
+     * should be left out of the result so that the request will be retried.
+     *
+     * @param keys the set of keys from the associated request
+     * @param response the response received from the broker
+     *
+     * @return a result indicating which keys mapped successfully to a brokerId and
+     *         which encountered a fatal error
+     */
+    LookupResult<T> handleResponse(Set<T> keys, AbstractResponse response);
+
+    class LookupResult<K> {
+        public final Map<K, Integer> mappedKeys;
+        public final Map<K, Throwable> failedKeys;
+
+        public LookupResult(
+            Map<K, Throwable> failedKeys,
+            Map<K, Integer> mappedKeys
+        ) {
+            this.failedKeys = Collections.unmodifiableMap(failedKeys);
+            this.mappedKeys = Collections.unmodifiableMap(mappedKeys);
+        }
+    }
+
+    interface RequestScope {
+        default OptionalInt destinationBrokerId() {
+            return OptionalInt.empty();
+        };

Review comment:
       unnecessary `;`

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/DescribeProducersOptions.java
##########
@@ -0,0 +1,63 @@
+/*
+ * 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.kafka.clients.admin;
+
+import org.apache.kafka.common.annotation.InterfaceStability;
+
+import java.util.Collection;
+import java.util.Objects;
+import java.util.OptionalInt;
+
+/**
+ * Options for {@link Admin#describeProducers(Collection)}.
+ *
+ * The API of this class is evolving, see {@link Admin} for details.
+ */
+@InterfaceStability.Evolving
+public class DescribeProducersOptions extends AbstractOptions<DescribeProducersOptions> {
+    private OptionalInt brokerId = OptionalInt.empty();
+
+    public DescribeProducersOptions setBrokerId(int brokerId) {
+        this.brokerId = OptionalInt.of(brokerId);
+        return this;
+    }
+
+    public OptionalInt brokerId() {
+        return brokerId;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        DescribeProducersOptions that = (DescribeProducersOptions) o;
+        return Objects.equals(brokerId, that.brokerId);

Review comment:
       Should it compare `timeoutMs`?

##########
File path: clients/src/main/java/org/apache/kafka/clients/admin/internals/AdminApiHandler.java
##########
@@ -0,0 +1,127 @@
+/*
+ * 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.kafka.clients.admin.internals;
+
+import org.apache.kafka.common.requests.AbstractRequest;
+import org.apache.kafka.common.requests.AbstractResponse;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.Set;
+
+public interface AdminApiHandler<K, V> {
+
+    /**
+     * Get a user-friendly name for the API this handler is implementing.
+     */
+    String apiName();
+
+    /**
+     * Initialize the set of keys required to handle this API and how the driver
+     * should map them to the broker that will handle the request for these keys.
+     *
+     * Two mapping types are supported:
+     *
+     * - Static mapping: when the brokerId is known ahead of time
+     * - Dynamic mapping: when the brokerId must be discovered dynamically
+     *
+     * @return the key mappings
+     */
+    KeyMappings<K> initializeKeys();
+
+    /**
+     * Build the fulfillment request. The set of keys are derived during the Lookup stage
+     * as the set of keys which all map to the same destination broker.
+     *
+     * @param brokerId the target brokerId for the request
+     * @param keys the set of keys that should be handled by this request
+     *
+     * @return a builder for the request containing the given keys
+     */
+    AbstractRequest.Builder<?> buildRequest(Integer brokerId, Set<K> keys);
+
+    /**
+     * Callback that is invoked when a Fulfillment request returns successfully.
+     * The handler should parse the response, check for errors, and return a
+     * result which indicates which keys (if any) have either been completed or
+     * failed with an unrecoverable error.
+     *
+     * It is also possible that the response indicates an incorrect target brokerId
+     * (e.g. in the case of a NotLeader error when the request is bound for a partition
+     * leader). In this case the key will be "unmapped" from the target brokerId
+     * and lookup will be retried.
+     *
+     * Note that keys which received a retriable error should be left out of the
+     * result. They will be retried automatically.
+     *
+     * @param brokerId the brokerId that the associated request was sent to
+     * @param keys the set of keys from the associated request
+     * @param response the response received from the broker
+     *
+     * @return result indicating key complation, failure, and unmapping
+     */
+    ApiResult<K, V> handleResponse(Integer brokerId, Set<K> keys, AbstractResponse response);
+
+    class KeyMappings<K> {
+        public final Optional<StaticKeyMapping<K>> staticMapping;
+        public final Optional<DynamicKeyMapping<K>> dynamicMapping;
+
+        public KeyMappings(
+            Optional<StaticKeyMapping<K>> staticMapping,
+            Optional<DynamicKeyMapping<K>> dynamicMapping
+        ) {
+            this.staticMapping = staticMapping;
+            this.dynamicMapping = dynamicMapping;
+        }
+    }
+
+    class StaticKeyMapping<K> {
+        public final Map<K, Integer> keys;
+
+        public StaticKeyMapping(Map<K, Integer> keys) {
+            this.keys = keys;
+        }
+    }
+
+    class DynamicKeyMapping<K> {
+        public final Set<K> keys;
+        public final AdminApiLookupStrategy<K> lookupStrategy;
+
+        public DynamicKeyMapping(Set<K> keys, AdminApiLookupStrategy<K> lookupStrategy) {
+            this.keys = keys;

Review comment:
       wrap it to unmodified collection?




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