[GitHub] [pulsar] AnonHxy commented on a diff in pull request #17822: [improve][java-client]Add init capactiy for messages in BatchMessageContainerImpl

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

AnonHxy commented on code in PR #17822:
URL: https://github.com/apache/pulsar/pull/17822#discussion_r979352513


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pulsar-client/src/main/java/org/apache/pulsar/client/impl/BatchMessageContainerImpl.java:
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@@ -168,12 +168,13 @@ private ByteBuf getCompressedBatchMetadataAndPayload() {
         // Update the current max batch size using the uncompressed size, which is what we need in any case to
         // accumulate the batch content
         maxBatchSize = Math.max(maxBatchSize, uncompressedSize);
+        maxMessagesNum = Math.max(maxMessagesNum, numMessagesInBatch);
         return compressedPayload;
     }
 
     @Override
     public void clear() {
-        messages = new ArrayList<>();
+        messages = new ArrayList<>(maxMessagesNum);

Review Comment:
   If using `message.clear()`, there will be some cpu overhead I think.  We must check if `messages.size == maxMessageNum`, and the clear() method will loop all the elements in the arrayList:
   ```
    public void clear() {
           modCount++;
           final Object[] es = elementData;
           for (int to = size, i = size = 0; i < to; i++)
               es[i] = null;
       }
   ```



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