[GitHub] [pulsar] merlimat commented on a change in pull request #6362: [ClientAPI]Fix hasMessageAvailable()

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

merlimat commented on a change in pull request #6362: [ClientAPI]Fix hasMessageAvailable()
URL: https://github.com/apache/pulsar/pull/6362#discussion_r386619487
 
 

 ##########
 File path: pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java
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 @@ -1396,22 +1401,83 @@ protected void handleGetLastMessageId(CommandGetLastMessageId getLastMessageId)
             Topic topic = consumer.getSubscription().getTopic();
             Position position = topic.getLastMessageId();
             int partitionIndex = TopicName.getPartitionIndex(topic.getName());
-            if (log.isDebugEnabled()) {
-                log.debug("[{}] [{}][{}] Get LastMessageId {} partitionIndex {}", remoteAddress,
-                    topic.getName(), consumer.getSubscription().getName(), position, partitionIndex);
-            }
-            MessageIdData messageId = MessageIdData.newBuilder()
-                .setLedgerId(((PositionImpl)position).getLedgerId())
-                .setEntryId(((PositionImpl)position).getEntryId())
-                .setPartition(partitionIndex)
-                .build();
 
-            ctx.writeAndFlush(Commands.newGetLastMessageIdResponse(requestId, messageId));
+            getLargestBatchIndexWhenPossible(
+                    topic,
+                    (PositionImpl) position,
+                    partitionIndex,
+                    requestId,
+                    consumer.getSubscription().getName());
+
         } else {
             ctx.writeAndFlush(Commands.newError(getLastMessageId.getRequestId(), ServerError.MetadataError, "Consumer not found"));
         }
     }
 
+    private void getLargestBatchIndexWhenPossible(
+            Topic topic,
+            PositionImpl position,
+            int partitionIndex,
+            long requestId,
+            String subscriptionName) {
+
+        PersistentTopic persistentTopic = (PersistentTopic) topic;
+        ManagedLedgerImpl ml = (ManagedLedgerImpl) persistentTopic.getManagedLedger();
+
+        // If it's not pointing to a valid entry, respond messageId of the current position.
+        if (position.getEntryId() == -1) {
+            MessageIdData messageId = MessageIdData.newBuilder()
+                    .setLedgerId(position.getLedgerId())
+                    .setEntryId(position.getEntryId())
+                    .setPartition(partitionIndex).build();
+
+            ctx.writeAndFlush(Commands.newGetLastMessageIdResponse(requestId, messageId));
+        }
+
+        // For a valid position, we read the entry out and parse the batch size from its metadata.
+        CompletableFuture<Entry> entryFuture = new CompletableFuture<>();
+        ml.asyncReadEntry(position, new AsyncCallbacks.ReadEntryCallback() {
 
 Review comment:
   Ideally we should be avoiding this read by just recording the number of messages in the last batch, along with the current position.

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