[GitHub] [pulsar] BewareMyPower commented on a diff in pull request #18877: [fix] [broker] getLastMessageId returns a wrong batch index of last message if enabled read compacted

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

BewareMyPower commented on code in PR #18877:
URL: https://github.com/apache/pulsar/pull/18877#discussion_r1045275815


##########
pulsar-broker/src/main/java/org/apache/pulsar/broker/service/ServerCnx.java:
##########
@@ -2017,6 +2027,25 @@ private void handleLastMessageIdFromCompactedLedger(PersistentTopic persistentTo
         });
     }
 
+    private int calculateTheLastBatchIndexInBatch(MessageMetadata metadata, ByteBuf payload) throws IOException {
+        int batchSize = metadata.getNumMessagesInBatch();
+        if (batchSize <= 1){
+            return -1;
+        }
+        SingleMessageMetadata singleMessageMetadata = new SingleMessageMetadata();
+        int lastBatchIndexInBatch = -1;
+        for (int i = 0; i < batchSize; i++){
+            ByteBuf singleMessagePayload =
+                    Commands.deSerializeSingleMessageInBatch(payload, singleMessageMetadata, i, batchSize);
+            singleMessagePayload.release();
+            if (singleMessageMetadata.isCompactedOut()){
+                continue;
+            }
+            lastBatchIndexInBatch = i;
+        }
+        return lastBatchIndexInBatch;

Review Comment:
   ```suggestion
           for (int i = batchSize - 1; i >= 0; i--) {
               ByteBuf singleMessagePayload =
                       Commands.deSerializeSingleMessageInBatch(payload, singleMessageMetadata, i, batchSize);
               singleMessagePayload.release();
               if (!singleMessageMetadata.isCompactedOut()) {
                   return i;
               }
           }
           return -1;
   ```
   
   Use a reversed iteration to avoid unnecessary iterations because the most of time



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