[GitHub] [kafka] showuon commented on a change in pull request #11187: [WIP] KAFKA-5966: let CacheFunction#key return ByteBuffer

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showuon commented on a change in pull request #11187:
URL: https://github.com/apache/kafka/pull/11187#discussion_r684704566



##########
File path: 
streams/src/main/java/org/apache/kafka/streams/state/internals/MergedSortedCacheSessionStoreIterator.java
##########
@@ -45,8 +47,8 @@
 
     @Override
     Windowed<Bytes> deserializeCacheKey(final Bytes cacheKey) {
-        final byte[] binaryKey = cacheFunction.key(cacheKey).get();
-        final byte[] keyBytes = SessionKeySchema.extractKeyBytes(binaryKey);
+        final ByteBuffer binaryKey = cacheFunction.key(cacheKey);
+        final ByteBuffer keyBytes = 
SessionKeySchema.extractKeyBytes(binaryKey);
         final Window window = SessionKeySchema.extractWindow(binaryKey);

Review comment:
       This is a good example that we avoided unnecessary array copy.
   Before:
   1. `cacheFunction.key(cacheKey)`  -> do an array copy
   2. `SessionKeySchema.extractKeyBytes(binaryKey)` -> do an array copy
   
   After:
   1. `cacheFunction.key(cacheKey)`  -> no array copy, just return sliced byte 
buffer
   2. `SessionKeySchema.extractKeyBytes(binaryKey)` -> no array copy, just 
return sliced byte buffer
   




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