kafka-1984; java producer may miss an available partition; patched by Jun Rao; reviewed by Ewen Cheslack-Postava, Jay Kreps, and Guozhang Wang

clients/src/main/java/org/apache/kafka/clients/producer/internals/Partitioner.java

@@ -56,14 +56,15 @@ public class Partitioner {
                                                    + "].");
             return partition;
         } else if (key == null) {
-            // choose the next available node in a round-robin fashion
-            for (int i = 0; i < numPartitions; i++) {
-                int part = Utils.abs(counter.getAndIncrement()) % numPartitions;
-                if (partitions.get(part).leader() != null)
-                    return part;
+            int nextValue = counter.getAndIncrement();
+            List<PartitionInfo> availablePartitions = cluster.availablePartitionsForTopic(topic);
+            if (availablePartitions.size() > 0) {
+                int part = Utils.abs(nextValue) % availablePartitions.size();
+                return availablePartitions.get(part).partition();
+            } else {
+                // no partitions are available, give a non-available partition
+                return Utils.abs(nextValue) % numPartitions;
             }
-            // no partitions are available, give a non-available partition
-            return Utils.abs(counter.getAndIncrement()) % numPartitions;
         } else {
             // hash the key to choose a partition
             return Utils.abs(Utils.murmur2(key)) % numPartitions;

clients/src/main/java/org/apache/kafka/common/Cluster.java

@@ -25,6 +25,7 @@ public final class Cluster {
     private final List<Node> nodes;
     private final Map<TopicPartition, PartitionInfo> partitionsByTopicPartition;
     private final Map<String, List<PartitionInfo>> partitionsByTopic;
+    private final Map<String, List<PartitionInfo>> availablePartitionsByTopic;
     private final Map<Integer, List<PartitionInfo>> partitionsByNode;
     private final Map<Integer, Node> nodesById;
 
@@ -68,8 +69,18 @@ public final class Cluster {
             }
         }
         this.partitionsByTopic = new HashMap<String, List<PartitionInfo>>(partsForTopic.size());
-        for (Map.Entry<String, List<PartitionInfo>> entry : partsForTopic.entrySet())
-            this.partitionsByTopic.put(entry.getKey(), Collections.unmodifiableList(entry.getValue()));
+        this.availablePartitionsByTopic = new HashMap<String, List<PartitionInfo>>(partsForTopic.size());
+        for (Map.Entry<String, List<PartitionInfo>> entry : partsForTopic.entrySet()) {
+            String topic = entry.getKey();
+            List<PartitionInfo> partitionList = entry.getValue();
+            this.partitionsByTopic.put(topic, Collections.unmodifiableList(partitionList));
+            List<PartitionInfo> availablePartitions = new ArrayList<PartitionInfo>();
+            for (PartitionInfo part : partitionList) {
+                if (part.leader() != null)
+                    availablePartitions.add(part);
+            }
+            this.availablePartitionsByTopic.put(topic, Collections.unmodifiableList(availablePartitions));
+        }
         this.partitionsByNode = new HashMap<Integer, List<PartitionInfo>>(partsForNode.size());
         for (Map.Entry<Integer, List<PartitionInfo>> entry : partsForNode.entrySet())
             this.partitionsByNode.put(entry.getKey(), Collections.unmodifiableList(entry.getValue()));
@@ -143,6 +154,15 @@ public final class Cluster {
         return this.partitionsByTopic.get(topic);
     }
 
+    /**
+     * Get the list of available partitions for this topic
+     * @param topic The topic name
+     * @return A list of partitions
+     */
+    public List<PartitionInfo> availablePartitionsForTopic(String topic) {
+        return this.availablePartitionsByTopic.get(topic);
+    }
+
     /**
      * Get the list of partitions whose leader is this node
      * @param nodeId The node id

clients/src/test/java/org/apache/kafka/clients/producer/PartitionerTest.java

@@ -33,9 +33,10 @@ public class PartitionerTest {
     private Node node2 = new Node(2, "localhost", 101);
     private Node[] nodes = new Node[] {node0, node1, node2};
     private String topic = "test";
-    private List<PartitionInfo> partitions = asList(new PartitionInfo(topic, 0, node0, nodes, nodes),
-                                                    new PartitionInfo(topic, 1, node1, nodes, nodes),
-                                                    new PartitionInfo(topic, 2, null, nodes, nodes));
+    // Intentionally make the partition list not in partition order to test the edge cases.
+    private List<PartitionInfo> partitions = asList(new PartitionInfo(topic, 1, null, nodes, nodes),
+                                                    new PartitionInfo(topic, 2, node1, nodes, nodes),
+                                                    new PartitionInfo(topic, 0, node0, nodes, nodes));
     private Cluster cluster = new Cluster(asList(node0, node1, node2), partitions);
 
     @Test
@@ -50,19 +51,19 @@ public class PartitionerTest {
     }
 
     @Test
-    public void testRoundRobinIsStable() {
-        int startPart = partitioner.partition("test", null, null, cluster);
+    public void testRoundRobinWithUnavailablePartitions() {
+        // When there are some unavailable partitions, we want to make sure that (1) we always pick an available partition,
+        // and (2) the available partitions are selected in a round robin way.
+        int countForPart0 = 0;
+        int countForPart2 = 0;
         for (int i = 1; i <= 100; i++) {
-            int partition = partitioner.partition("test", null, null, cluster);
-            assertEquals("Should yield a different partition each call with round-robin partitioner", partition, (startPart + i) % 2);
-        }
-    }
-
-    @Test
-    public void testRoundRobinWithDownNode() {
-        for (int i = 0; i < partitions.size(); i++) {
             int part = partitioner.partition("test", null, null, cluster);
-            assertTrue("We should never choose a leader-less node in round robin", part >= 0 && part < 2);
+            assertTrue("We should never choose a leader-less node in round robin", part == 0 || part == 2);
+            if (part == 0)
+                countForPart0++;
+            else
+                countForPart2++;
         }
+        assertEquals("The distribution between two available partitions should be even", countForPart0, countForPart2);
     }
 }