ezhou413 commented on code in PR #23483:
URL: https://github.com/apache/kafka/pull/23483#discussion_r4319278497
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clients/src/main/java/org/apache/kafka/clients/producer/internals/ChunkedProducerBatch.java:
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@@ -74,17 +75,39 @@ int extensionBytesNeeded(long timestamp, byte[] key, byte[]
value, Header[] head
* {@code ChunkedRecordAccumulator.tryAppend}, which evaluates {@link
#extensionBytesNeeded}
* itself and attaches chunks before retrying, so repeating the check for
those would size the
* record a second time on every append for no added safety.
+ * <p>
+ * The check applies only to uncompressed batches, where the pre-size and
the demand are the same
+ * upper bound. For a compressed batch the demand scales with the topic's
compression ratio
+ * estimate, which can exceed 1.0 for incompressible data and can change
between pre-sizing and
+ * batch creation, so the pre-size is only a heuristic; any overshoot is
absorbed by the stream
+ * growing mid-write (see {@link ChunkedByteBufferOutputStream}).
+ * <p>
+ * If that growth had to fall back to the heap because the pool was
exhausted, the record is still
Review Comment:
Updated the comment
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