[GitHub] [flink] leonardBang commented on a diff in pull request #19456: [FLINK-27041][connector/kafka] Catch IllegalStateException in KafkaPartitionSplitReader.fetch() to handle no valid partition case

[GitBox <gi...@apache.org>]

leonardBang commented on code in PR #19456:
URL: https://github.com/apache/flink/pull/19456#discussion_r892310026


##########
flink-connectors/flink-connector-kafka/src/main/java/org/apache/flink/connector/kafka/source/reader/KafkaPartitionSplitReader.java:
##########
@@ -98,9 +98,16 @@ public RecordsWithSplitIds<ConsumerRecord<byte[], byte[]>> fetch() throws IOExce
         ConsumerRecords<byte[], byte[]> consumerRecords;
         try {
             consumerRecords = consumer.poll(Duration.ofMillis(POLL_TIMEOUT));
-        } catch (WakeupException we) {
-            return new KafkaPartitionSplitRecords(
-                    ConsumerRecords.empty(), kafkaSourceReaderMetrics);
+        } catch (WakeupException | IllegalStateException e) {
+            // IllegalStateException will be thrown if the consumer is not assigned any partitions.
+            // This happens if all assigned partitions are invalid or empty (starting offset >=

Review Comment:
    > all assigned partitions are invalid
   
   'all' should be 'some of'? 



##########
flink-connectors/flink-connector-kafka/src/test/java/org/apache/flink/connector/kafka/source/KafkaSourceITCase.java:
##########
@@ -443,13 +502,15 @@ public void invoke(PartitionAndValue value, Context context) {
                                 .add(partitionAndValue.value));
         resultPerPartition.forEach(
                 (tp, values) -> {
-                    int firstExpectedValue = Integer.parseInt(tp.substring(tp.indexOf('-') + 1));
+                    int firstExpectedValue =
+                            Integer.parseInt(tp.substring(tp.lastIndexOf('-') + 1));

Review Comment:
   we can add a note here:
   the elements of partition is an automatic integer sequence start from the partition number. 



##########
flink-connectors/flink-connector-kafka/src/test/java/org/apache/flink/connector/kafka/source/KafkaSourceITCase.java:
##########
@@ -309,6 +309,65 @@ public void processElement(
                             });
             env.execute();
         }
+
+        @Test
+        public void testConsumingEmptyTopic() throws Throwable {
+            String emptyTopic = "emptyTopic-" + UUID.randomUUID();
+            KafkaSourceTestEnv.createTestTopic(emptyTopic, 3, 1);
+            KafkaSource<PartitionAndValue> source =
+                    KafkaSource.<PartitionAndValue>builder()
+                            .setBootstrapServers(KafkaSourceTestEnv.brokerConnectionStrings)
+                            .setTopics(emptyTopic)
+                            .setGroupId("empty-topic-test")
+                            .setDeserializer(new TestingKafkaRecordDeserializationSchema(false))
+                            .setStartingOffsets(OffsetsInitializer.earliest())
+                            .setBounded(OffsetsInitializer.latest())
+                            .build();
+            StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+            env.setParallelism(1);
+            try (CloseableIterator<PartitionAndValue> iterator =
+                    env.fromSource(
+                                    source,
+                                    WatermarkStrategy.noWatermarks(),
+                                    "testConsumingEmptyTopic")
+                            .executeAndCollect()) {
+                assertThat(iterator.hasNext()).isFalse();
+            }
+        }
+
+        @Test
+        public void testConsumingTopicWithEmptyPartitions() throws Throwable {
+            String topicWithEmptyPartitions = "topicWithEmptyPartitions-" + UUID.randomUUID();
+            KafkaSourceTestEnv.createTestTopic(
+                    topicWithEmptyPartitions, KafkaSourceTestEnv.NUM_PARTITIONS, 1);
+            List<ProducerRecord<String, Integer>> records =
+                    KafkaSourceTestEnv.getRecordsForTopicWithoutTimestamp(topicWithEmptyPartitions);
+            // Only keep records in partition 5
+            int partitionWithRecords = 5;
+            records.removeIf(record -> record.partition() != partitionWithRecords);
+            KafkaSourceTestEnv.produceToKafka(records);
+            KafkaSourceTestEnv.setupEarliestOffsets(
+                    Collections.singletonList(
+                            new TopicPartition(topicWithEmptyPartitions, partitionWithRecords)));
+
+            KafkaSource<PartitionAndValue> source =
+                    KafkaSource.<PartitionAndValue>builder()
+                            .setBootstrapServers(KafkaSourceTestEnv.brokerConnectionStrings)
+                            .setTopics(topicWithEmptyPartitions)
+                            .setGroupId("topic-with-empty-partition-test")
+                            .setDeserializer(new TestingKafkaRecordDeserializationSchema(false))
+                            .setStartingOffsets(OffsetsInitializer.earliest())
+                            .setBounded(OffsetsInitializer.latest())
+                            .build();
+            StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
+            env.setParallelism(2);

Review Comment:
   Could we use default parallelism?
   What's the purpose to set different  parallelism in these test cases? 



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