Hotfix 0.4.161 stuck consumer metric and repair (#782)

* [server] Introduced a repair service for stuck shared consumer (#757) * [server] Introduced a repair service for stuck shared consumer Recently, we noticed that some shared consumers were stuck since they were blocked by producing to some non-existing topics, and many other store versions got affected since the stuck consumer is being shared by many other stores. This PR introduces a way to detect and repair stuck consumer for above situation. In the high level, there will be a thread periodically check whether consumer#poll is being invoked regularly or not, and if not, the thread will scan all the ingestion tasks to see whether they are producing to any non-existing topics or not. And for the store ingestion task, which is talking to some non-existing topic, the repair thread will try to close the stuck KafkaProducer and kill the corresponding ingestion task. This PR also checked the non-existing topics for a configurable duration to tolerate tranisent topic metadata propagaton delay. 5 new server configs: server.stuck.consumer.repair.enabled : default true server.stuck.consumer.repair.second : default 1 min server.stuck.consumer.repair.threshold.second : default 5 mins server.non.existing.topic.ingestion.task.kill.threshold.second: default 15 mins server.non.existing.topic.check.retry.interval.second: default 1 min 3 new server metrics: .StuckConsumerRepair--stuck_consumer_found.OccurrenceRate .StuckConsumerRepair--ingestion_task_repair.OccurrenceRate .StuckConsumerRepair--repair_failure.OccurrenceRate * [server][da-vinci] Construct the MaxElapsedTimeSinceLastPoll Gauge metric with function instead of value (#781) Constructing Venice Gauge metric with value is pointless; Venice Gauge metric can only work with function. * [client][server] Emit system store metric only for server (#764) [server][client] Emit system store metric only for server System store metrics are useful only in server side. This PR prevents emission of meta system store metrics in DaVinci/thin clients. Co-authored-by: Sourav Maji <[email protected]> --------- Co-authored-by: Min Huang <[email protected]> Co-authored-by: Sourav Maji <[email protected]> Co-authored-by: Sourav Maji <[email protected]>
linkedin · Dec 1, 2023 · 8abb661 · 8abb661
1 parent 9a2bf95
commit 8abb661
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diff --git a/clients/da-vinci-client/src/main/java/com/linkedin/davinci/config/VeniceServerConfig.java b/clients/da-vinci-client/src/main/java/com/linkedin/davinci/config/VeniceServerConfig.java
@@ -83,6 +83,8 @@
 import static com.linkedin.venice.ConfigKeys.SERVER_NETTY_IDLE_TIME_SECONDS;
 import static com.linkedin.venice.ConfigKeys.SERVER_NETTY_WORKER_THREADS;
 import static com.linkedin.venice.ConfigKeys.SERVER_NODE_CAPACITY_RCU;
+import static com.linkedin.venice.ConfigKeys.SERVER_NON_EXISTING_TOPIC_CHECK_RETRY_INTERNAL_SECOND;
+import static com.linkedin.venice.ConfigKeys.SERVER_NON_EXISTING_TOPIC_INGESTION_TASK_KILL_THRESHOLD_SECOND;
 import static com.linkedin.venice.ConfigKeys.SERVER_NUM_SCHEMA_FAST_CLASS_WARMUP;
 import static com.linkedin.venice.ConfigKeys.SERVER_OPTIMIZE_DATABASE_FOR_BACKUP_VERSION_ENABLED;
 import static com.linkedin.venice.ConfigKeys.SERVER_OPTIMIZE_DATABASE_FOR_BACKUP_VERSION_NO_READ_THRESHOLD_SECONDS;
@@ -110,6 +112,9 @@
 import static com.linkedin.venice.ConfigKeys.SERVER_SSL_HANDSHAKE_THREAD_POOL_SIZE;
 import static com.linkedin.venice.ConfigKeys.SERVER_STOP_CONSUMPTION_TIMEOUT_IN_SECONDS;
 import static com.linkedin.venice.ConfigKeys.SERVER_STORE_TO_EARLY_TERMINATION_THRESHOLD_MS_MAP;
+import static com.linkedin.venice.ConfigKeys.SERVER_STUCK_CONSUMER_REPAIR_ENABLED;
+import static com.linkedin.venice.ConfigKeys.SERVER_STUCK_CONSUMER_REPAIR_INTERVAL_SECOND;
+import static com.linkedin.venice.ConfigKeys.SERVER_STUCK_CONSUMER_REPAIR_THRESHOLD_SECOND;
 import static com.linkedin.venice.ConfigKeys.SERVER_SYSTEM_STORE_PROMOTION_TO_LEADER_REPLICA_DELAY_SECONDS;
 import static com.linkedin.venice.ConfigKeys.SERVER_UNSUB_AFTER_BATCHPUSH;
 import static com.linkedin.venice.ConfigKeys.SEVER_CALCULATE_QUOTA_USAGE_BASED_ON_PARTITIONS_ASSIGNMENT_ENABLED;
@@ -445,6 +450,12 @@ public class VeniceServerConfig extends VeniceClusterConfig {
 
   private final long ingestionHeartbeatIntervalMs;
 
+  private final boolean stuckConsumerRepairEnabled;
+  private final int stuckConsumerRepairIntervalSecond;
+  private final int stuckConsumerDetectionRepairThresholdSecond;
+  private final int nonExistingTopicIngestionTaskKillThresholdSecond;
+  private final int nonExistingTopicCheckRetryIntervalSecond;
+
   public VeniceServerConfig(VeniceProperties serverProperties) throws ConfigurationException {
     this(serverProperties, Collections.emptyMap());
   }
@@ -731,6 +742,21 @@ public VeniceServerConfig(VeniceProperties serverProperties, Map<String, Map<Str
     metaStoreWriterCloseConcurrency = serverProperties.getInt(META_STORE_WRITER_CLOSE_CONCURRENCY, -1);
     ingestionHeartbeatIntervalMs =
         serverProperties.getLong(SERVER_INGESTION_HEARTBEAT_INTERVAL_MS, TimeUnit.MINUTES.toMillis(1));
+
+    stuckConsumerRepairEnabled = serverProperties.getBoolean(SERVER_STUCK_CONSUMER_REPAIR_ENABLED, true);
+    stuckConsumerRepairIntervalSecond = serverProperties.getInt(SERVER_STUCK_CONSUMER_REPAIR_INTERVAL_SECOND, 60);
+    stuckConsumerDetectionRepairThresholdSecond =
+        serverProperties.getInt(SERVER_STUCK_CONSUMER_REPAIR_THRESHOLD_SECOND, 5 * 60); // 5 mins
+    if (stuckConsumerRepairEnabled && stuckConsumerDetectionRepairThresholdSecond < stuckConsumerRepairIntervalSecond) {
+      throw new VeniceException(
+          "Config for " + SERVER_STUCK_CONSUMER_REPAIR_THRESHOLD_SECOND + ": "
+              + stuckConsumerDetectionRepairThresholdSecond + " should be equal to or larger than "
+              + SERVER_STUCK_CONSUMER_REPAIR_INTERVAL_SECOND + ": " + stuckConsumerRepairIntervalSecond);
+    }
+    nonExistingTopicIngestionTaskKillThresholdSecond =
+        serverProperties.getInt(SERVER_NON_EXISTING_TOPIC_INGESTION_TASK_KILL_THRESHOLD_SECOND, 15 * 60); // 15 mins
+    nonExistingTopicCheckRetryIntervalSecond =
+        serverProperties.getInt(SERVER_NON_EXISTING_TOPIC_CHECK_RETRY_INTERNAL_SECOND, 60); // 1min
   }
 
   long extractIngestionMemoryLimit(
@@ -1284,4 +1310,24 @@ public int getMetaStoreWriterCloseConcurrency() {
   public long getIngestionHeartbeatIntervalMs() {
     return ingestionHeartbeatIntervalMs;
   }
+
+  public boolean isStuckConsumerRepairEnabled() {
+    return stuckConsumerRepairEnabled;
+  }
+
+  public int getStuckConsumerRepairIntervalSecond() {
+    return stuckConsumerRepairIntervalSecond;
+  }
+
+  public int getStuckConsumerDetectionRepairThresholdSecond() {
+    return stuckConsumerDetectionRepairThresholdSecond;
+  }
+
+  public int getNonExistingTopicIngestionTaskKillThresholdSecond() {
+    return nonExistingTopicIngestionTaskKillThresholdSecond;
+  }
+
+  public int getNonExistingTopicCheckRetryIntervalSecond() {
+    return nonExistingTopicCheckRetryIntervalSecond;
+  }
 }
diff --git a/...nci-client/src/main/java/com/linkedin/davinci/kafka/consumer/AggKafkaConsumerService.java b/...nci-client/src/main/java/com/linkedin/davinci/kafka/consumer/AggKafkaConsumerService.java
@@ -4,6 +4,7 @@
 
 import com.linkedin.davinci.config.VeniceServerConfig;
 import com.linkedin.davinci.ingestion.consumption.ConsumedDataReceiver;
+import com.linkedin.davinci.stats.StuckConsumerRepairStats;
 import com.linkedin.venice.exceptions.VeniceException;
 import com.linkedin.venice.kafka.TopicManagerRepository;
 import com.linkedin.venice.kafka.protocol.KafkaMessageEnvelope;
@@ -16,15 +17,24 @@
 import com.linkedin.venice.pubsub.api.PubSubTopicPartition;
 import com.linkedin.venice.service.AbstractVeniceService;
 import com.linkedin.venice.throttle.EventThrottler;
+import com.linkedin.venice.utils.DaemonThreadFactory;
 import com.linkedin.venice.utils.SystemTime;
+import com.linkedin.venice.utils.Utils;
 import com.linkedin.venice.utils.concurrent.VeniceConcurrentHashMap;
 import io.tehuti.metrics.MetricsRepository;
 import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import java.util.HashMap;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Consumer;
 import java.util.function.Function;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
@@ -56,6 +66,9 @@ public class AggKafkaConsumerService extends AbstractVeniceService {
   private final TopicManagerRepository.SSLPropertiesSupplier sslPropertiesSupplier;
   private final Function<String, String> kafkaClusterUrlResolver;
 
+  private final Map<String, StoreIngestionTask> versionTopicStoreIngestionTaskMapping = new VeniceConcurrentHashMap<>();
+  private ScheduledExecutorService stuckConsumerRepairExecutorService;
+
   public AggKafkaConsumerService(
       final PubSubConsumerAdapterFactory consumerFactory,
       TopicManagerRepository.SSLPropertiesSupplier sslPropertiesSupplier,
@@ -65,7 +78,8 @@ public AggKafkaConsumerService(
       KafkaClusterBasedRecordThrottler kafkaClusterBasedRecordThrottler,
       final MetricsRepository metricsRepository,
       TopicExistenceChecker topicExistenceChecker,
-      final PubSubMessageDeserializer pubSubDeserializer) {
+      final PubSubMessageDeserializer pubSubDeserializer,
+      Consumer<String> killIngestionTaskRunnable) {
     this.consumerFactory = consumerFactory;
     this.readCycleDelayMs = serverConfig.getKafkaReadCycleDelayMs();
     this.numOfConsumersPerKafkaCluster = serverConfig.getConsumerPoolSizePerKafkaCluster();
@@ -83,6 +97,26 @@ public AggKafkaConsumerService(
     this.pubSubDeserializer = pubSubDeserializer;
     this.sslPropertiesSupplier = sslPropertiesSupplier;
     this.kafkaClusterUrlResolver = serverConfig.getKafkaClusterUrlResolver();
+
+    if (serverConfig.isStuckConsumerRepairEnabled()) {
+      this.stuckConsumerRepairExecutorService = Executors.newSingleThreadScheduledExecutor(
+          new DaemonThreadFactory(this.getClass().getName() + "-StuckConsumerRepair"));
+      int intervalInSeconds = serverConfig.getStuckConsumerRepairIntervalSecond();
+      this.stuckConsumerRepairExecutorService.scheduleAtFixedRate(
+          getStuckConsumerDetectionAndRepairRunnable(
+              kafkaServerToConsumerServiceMap,
+              versionTopicStoreIngestionTaskMapping,
+              TimeUnit.SECONDS.toMillis(serverConfig.getStuckConsumerDetectionRepairThresholdSecond()),
+              TimeUnit.SECONDS.toMillis(serverConfig.getNonExistingTopicIngestionTaskKillThresholdSecond()),
+              TimeUnit.SECONDS.toMillis(serverConfig.getNonExistingTopicCheckRetryIntervalSecond()),
+              new StuckConsumerRepairStats(metricsRepository),
+              killIngestionTaskRunnable),
+          intervalInSeconds,
+          intervalInSeconds,
+          TimeUnit.SECONDS);
+      LOGGER.info("Started stuck consumer repair service with checking interval: {} seconds", intervalInSeconds);
+    }
+
     LOGGER.info("Successfully initialized AggKafkaConsumerService");
   }
 
@@ -100,6 +134,106 @@ public void stopInner() throws Exception {
     for (KafkaConsumerService consumerService: kafkaServerToConsumerServiceMap.values()) {
       consumerService.stop();
     }
+    if (this.stuckConsumerRepairExecutorService != null) {
+      this.stuckConsumerRepairExecutorService.shutdownNow();
+    }
+  }
+
+  protected static Runnable getStuckConsumerDetectionAndRepairRunnable(
+      Map<String, KafkaConsumerService> kafkaServerToConsumerServiceMap,
+      Map<String, StoreIngestionTask> versionTopicStoreIngestionTaskMapping,
+      long stuckConsumerRepairThresholdMs,
+      long nonExistingTopicIngestionTaskKillThresholdMs,
+      long nonExistingTopicRetryIntervalMs,
+      StuckConsumerRepairStats stuckConsumerRepairStats,
+      Consumer<String> killIngestionTaskRunnable) {
+    return () -> {
+      /**
+       * The following logic can be further optimized in the following way:
+       * 1. If the max delay of previous run is much smaller than the threshold.
+       * 2. In the next run, the max possible delay will be schedule interval + previous max delay ms, and if it is
+       * still below the threshold, this function can return directly.
+       * We are not adopting such optimization right now because:
+       * 1. Extra state to maintain.
+       * 2. The schedule interval is supposed to be high.
+       * 3. The check is cheap when there is no stuck consumer.
+       */
+      boolean scanStoreIngestionTaskToFixStuckConsumer = false;
+      for (KafkaConsumerService consumerService: kafkaServerToConsumerServiceMap.values()) {
+        long maxDelayMs = consumerService.getMaxElapsedTimeMSSinceLastPollInConsumerPool();
+        if (maxDelayMs >= stuckConsumerRepairThresholdMs) {
+          scanStoreIngestionTaskToFixStuckConsumer = true;
+          LOGGER.warn("Found some consumer has stuck for {} ms, will start the repairing procedure", maxDelayMs);
+          break;
+        }
+      }
+      if (!scanStoreIngestionTaskToFixStuckConsumer) {
+        return;
+      }
+      stuckConsumerRepairStats.recordStuckConsumerFound();
+
+      /**
+       * Collect a list of SITs, whose version topic doesn't exist by checking {@link StoreIngestionTask#isProducingVersionTopicHealthy()},
+       * and this function will continue to check the version topic healthiness for a period of {@link nonExistingTopicIngestionTaskKillThresholdMs}
+       * to tolerate transient topic discovery issue.
+       */
+      Map<String, StoreIngestionTask> versionTopicIngestionTaskMappingForNonExistingTopic = new HashMap<>();
+      versionTopicStoreIngestionTaskMapping.forEach((vt, sit) -> {
+        try {
+          if (!sit.isProducingVersionTopicHealthy()) {
+            versionTopicIngestionTaskMappingForNonExistingTopic.put(vt, sit);
+            LOGGER.warn("The producing version topic:{} is not healthy", vt);
+          }
+        } catch (Exception e) {
+          LOGGER.error("Got exception while checking topic existence for version topic: {}", vt, e);
+        }
+      });
+      int maxAttempts =
+          (int) Math.ceil((double) nonExistingTopicIngestionTaskKillThresholdMs / nonExistingTopicRetryIntervalMs);
+      for (int cnt = 0; cnt < maxAttempts; ++cnt) {
+        Iterator<Map.Entry<String, StoreIngestionTask>> iterator =
+            versionTopicIngestionTaskMappingForNonExistingTopic.entrySet().iterator();
+        while (iterator.hasNext()) {
+          Map.Entry<String, StoreIngestionTask> entry = iterator.next();
+          String versionTopic = entry.getKey();
+          StoreIngestionTask sit = entry.getValue();
+          try {
+            if (sit.isProducingVersionTopicHealthy()) {
+              /**
+               * If the version topic becomes available after retries, remove it from the tracking map.
+               */
+              iterator.remove();
+              LOGGER.info("The producing version topic:{} becomes healthy", versionTopic);
+            }
+          } catch (Exception e) {
+            LOGGER.error("Got exception while checking topic existence for version topic: {}", versionTopic, e);
+          } finally {
+            Utils.sleep(nonExistingTopicRetryIntervalMs);
+          }
+        }
+      }
+
+      AtomicBoolean repairSomeIngestionTask = new AtomicBoolean(false);
+      versionTopicIngestionTaskMappingForNonExistingTopic.forEach((vt, sit) -> {
+        LOGGER.warn(
+            "The ingestion topics (version topic) are not healthy for "
+                + "store version: {}, will kill the ingestion task to try to unblock shared consumer",
+            vt);
+        /**
+         * The following function call will interrupt all the stuck {@link org.apache.kafka.clients.producer.KafkaProducer#send} call
+         * to non-existing topics.
+         */
+        sit.closeVeniceWriters(false);
+        killIngestionTaskRunnable.accept(vt);
+        repairSomeIngestionTask.set(true);
+        stuckConsumerRepairStats.recordIngestionTaskRepair();
+      });
+      if (!repairSomeIngestionTask.get()) {
+        LOGGER.error(
+            "Didn't find any suspicious ingestion task, and please contact developers to investigate it further");
+        stuckConsumerRepairStats.recordRepairFailure();
+      }
+    };
   }
 
   /**
@@ -235,6 +369,8 @@ public ConsumedDataReceiver<List<PubSubMessage<KafkaKey, KafkaMessageEnvelope, L
 
     consumerService.startConsumptionIntoDataReceiver(pubSubTopicPartition, lastOffset, dataReceiver);
 
+    versionTopicStoreIngestionTaskMapping.put(storeIngestionTask.getVersionTopic().getName(), storeIngestionTask);
+
     return dataReceiver;
   }
 
@@ -260,6 +396,7 @@ public long getLatestOffsetFor(
    */
   void unsubscribeAll(PubSubTopic versionTopic) {
     kafkaServerToConsumerServiceMap.values().forEach(consumerService -> consumerService.unsubscribeAll(versionTopic));
+    versionTopicStoreIngestionTaskMapping.remove(versionTopic.getName());
   }
 
   void pauseConsumerFor(PubSubTopic versionTopic, PubSubTopicPartition pubSubTopicPartition) {

diff --git a/...-vinci-client/src/main/java/com/linkedin/davinci/kafka/consumer/KafkaConsumerService.java b/...-vinci-client/src/main/java/com/linkedin/davinci/kafka/consumer/KafkaConsumerService.java
@@ -116,7 +116,7 @@ protected KafkaConsumerService(
         : createKafkaConsumerServiceStats(
             metricsRepository,
             kafkaClusterAlias,
-            this::getMaxElapsedTimeSinceLastPollInConsumerPool);
+            this::getMaxElapsedTimeMSSinceLastPollInConsumerPool);
     for (int i = 0; i < numOfConsumersPerKafkaCluster; ++i) {
       /**
        * We need to assign a unique client id across all the storage nodes, otherwise, they will fail into the same throttling bucket.
@@ -324,7 +324,7 @@ private KafkaConsumerServiceStats createKafkaConsumerServiceStats(
         getMaxElapsedTimeSinceLastPollInConsumerPool);
   }
 
-  private long getMaxElapsedTimeSinceLastPollInConsumerPool() {
+  public long getMaxElapsedTimeMSSinceLastPollInConsumerPool() {
     long maxElapsedTimeSinceLastPollInConsumerPool = -1;
     int slowestTaskId = -1;
     long elapsedTimeSinceLastPoll;

diff --git a/...-client/src/main/java/com/linkedin/davinci/kafka/consumer/KafkaStoreIngestionService.java b/...-client/src/main/java/com/linkedin/davinci/kafka/consumer/KafkaStoreIngestionService.java
@@ -448,7 +448,8 @@ public void handleStoreDeleted(Store store) {
         kafkaClusterBasedRecordThrottler,
         metricsRepository,
         new MetadataRepoBasedTopicExistingCheckerImpl(this.getMetadataRepo()),
-        pubSubDeserializer);
+        pubSubDeserializer,
+        (topicName) -> this.killConsumptionTask(topicName));
     /**
      * After initializing a {@link AggKafkaConsumerService} service, it doesn't contain KafkaConsumerService yet until
      * a new Kafka cluster is registered; here we explicitly create KafkaConsumerService for the local Kafka cluster.

diff --git a/...t/src/main/java/com/linkedin/davinci/kafka/consumer/LeaderFollowerStoreIngestionTask.java b/...t/src/main/java/com/linkedin/davinci/kafka/consumer/LeaderFollowerStoreIngestionTask.java
@@ -282,7 +282,7 @@ public LeaderFollowerStoreIngestionTask(
   }
 
   @Override
-  protected void closeVeniceWriters(boolean doFlush) {
+  public void closeVeniceWriters(boolean doFlush) {
     if (veniceWriter.isPresent()) {
       veniceWriter.get().close(doFlush);
     }

diff --git a/...da-vinci-client/src/main/java/com/linkedin/davinci/kafka/consumer/StoreIngestionTask.java b/...da-vinci-client/src/main/java/com/linkedin/davinci/kafka/consumer/StoreIngestionTask.java
@@ -1390,6 +1390,13 @@ public void run() {
       LOGGER.info("{} has been killed.", consumerTaskId);
       statusReportAdapter.reportKilled(partitionConsumptionStateMap.values(), e);
       doFlush = false;
+      if (isCurrentVersion.getAsBoolean()) {
+        /**
+         * Current version can be killed if {@link AggKafkaConsumerService} discovers there are some issues with
+         * the producing topics, and here will report metrics for such case.
+         */
+        handleIngestionException(e);
+      }
     } catch (VeniceChecksumException e) {
       /**
        * It's possible to receive checksum verification failure exception here from the above syncOffset() call.
@@ -1521,7 +1528,7 @@ private void internalClose(boolean doFlush) {
     LOGGER.info("Store ingestion task for store: {} is closed", kafkaVersionTopic);
   }
 
-  protected void closeVeniceWriters(boolean doFlush) {
+  public void closeVeniceWriters(boolean doFlush) {
   }
 
   protected void closeVeniceViewWriters() {
@@ -3387,6 +3394,10 @@ public PubSubTopic getVersionTopic() {
     return versionTopic;
   }
 
+  public PubSubTopic getRealtimeTopic() {
+    return realTimeTopic;
+  }
+
   public boolean isMetricsEmissionEnabled() {
     return emitMetrics.get();
   }
@@ -3770,4 +3781,21 @@ protected boolean shouldUpdateUpstreamOffset(PubSubMessage<KafkaKey, KafkaMessag
   protected void maybeSendIngestionHeartbeat() {
     // No op, heartbeat is only useful for L/F hybrid stores.
   }
+
+  /**
+   * This function is checking the following conditions:
+   * 1. Whether the version topic exists or not.
+   */
+  public boolean isProducingVersionTopicHealthy() {
+    if (isDaVinciClient) {
+      /**
+       * DaVinci doesn't produce to any topics.
+       */
+      return true;
+    }
+    if (!topicManagerRepository.getTopicManager().containsTopic(this.versionTopic)) {
+      return false;
+    }
+    return true;
+  }
 }
diff --git a/...s/da-vinci-client/src/main/java/com/linkedin/davinci/stats/KafkaConsumerServiceStats.java b/...s/da-vinci-client/src/main/java/com/linkedin/davinci/stats/KafkaConsumerServiceStats.java
@@ -49,7 +49,7 @@ public KafkaConsumerServiceStats(
      */
     registerSensor(
         "max_elapsed_time_since_last_successful_poll",
-        new Gauge(getMaxElapsedTimeSinceLastPollInConsumerPool.getAsLong()));
+        new Gauge(() -> getMaxElapsedTimeSinceLastPollInConsumerPool.getAsLong()));
     // consumer record number per second returned by Kafka consumer poll.
     pollResultNumSensor = registerSensor("consumer_poll_result_num", new Avg(), new Total());
     pollNonZeroResultNumSensor = registerSensor("consumer_poll_non_zero_result_num", new Avg(), new Total());