Improve logging in the consumer for epoch updates (#6879)

clients/src/main/java/org/apache/kafka/clients/Metadata.java

@@ -177,7 +177,7 @@ public class Metadata implements Closeable {
             }
             return true;
         } else {
-            log.debug("Not replacing existing epoch {} with new epoch {}", oldEpoch, epoch);
+            log.debug("Not replacing existing epoch {} with new epoch {} for partition {}", oldEpoch, epoch, topicPartition);
             return false;
         }
     }

clients/src/main/java/org/apache/kafka/clients/MetadataCache.java

@@ -137,7 +137,10 @@ public class MetadataCache {
     @Override
     public String toString() {
         return "MetadataCache{" +
-                "cluster=" + cluster() +
+                "clusterId='" + clusterId + '\'' +
+                ", nodes=" + nodes +
+                ", partitions=" + metadataByPartition.values() +
+                ", controller=" + controller +
                 '}';
     }
 

clients/src/main/java/org/apache/kafka/clients/consumer/internals/Fetcher.java

@@ -861,13 +861,14 @@ public class Fetcher<K, V> implements Closeable {
         final Map<TopicPartition, ListOffsetRequest.PartitionData> partitionDataMap = new HashMap<>();
         for (Map.Entry<TopicPartition, Long> entry: timestampsToSearch.entrySet()) {
             TopicPartition tp  = entry.getKey();
+            Long offset = entry.getValue();
             Optional<MetadataCache.PartitionInfoAndEpoch> currentInfo = metadata.partitionInfoIfCurrent(tp);
             if (!currentInfo.isPresent()) {
-                log.debug("Leader for partition {} is unknown for fetching offset", tp);
+                log.debug("Leader for partition {} is unknown for fetching offset {}", tp, offset);
                 metadata.requestUpdate();
                 partitionsToRetry.add(tp);
             } else if (currentInfo.get().partitionInfo().leader() == null) {
-                log.debug("Leader for partition {} is unavailable for fetching offset", tp);
+                log.debug("Leader for partition {} is unavailable for fetching offset {}", tp, offset);
                 metadata.requestUpdate();
                 partitionsToRetry.add(tp);
             } else if (client.isUnavailable(currentInfo.get().partitionInfo().leader())) {
@@ -881,7 +882,7 @@ public class Fetcher<K, V> implements Closeable {
                 partitionsToRetry.add(tp);
             } else {
                 partitionDataMap.put(tp,
-                        new ListOffsetRequest.PartitionData(entry.getValue(), Optional.of(currentInfo.get().epoch())));
+                        new ListOffsetRequest.PartitionData(offset, Optional.of(currentInfo.get().epoch())));
             }
         }
         return regroupPartitionMapByNode(partitionDataMap);