Kafka endOffset

endOffsets()

🔢 1. Understanding endOffsets()

When you call:

long endOffset = consumer.endOffsets(List.of(tp)).get(tp);

You get the next offset after the last available message in that partition.

Think of endOffset as a marker:
“If a new message arrives, this is the offset it will be assigned.”

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🧠 Example:

Message	Offset
A	0
B	1
C	2

• endOffset = 3 (no message at offset 3 yet)

• So to read last message, we must seek to endOffset - 1 = 2

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🔍 Why Not Use endOffset Directly?

If you call:

consumer.seek(tp, endOffset); // BAD!

It will position the consumer after the last message, and poll() will return nothing, because there's nothing at that offset yet.

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✅ Summary

Offset	Meaning
currentOffset	Where the next poll() will start
endOffset	The next available offset, NOT the last existing record
endOffset - 1	Points to the actual last message in the topic/partition

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🧠 Interview Line:

“Kafka offsets are forward-pointing. The endOffset indicates where the next message will be written, not where the last message lives. So to retrieve the last message, we seek to endOffset - 1.”

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Let me know if you want this as a diagram or visual timeline — it's perfect for interview slides.