Scanteianu commented on code in PR #12753:
URL: https://github.com/apache/kafka/pull/12753#discussion_r1048113614
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clients/src/main/java/org/apache/kafka/clients/consumer/KafkaConsumer.java:
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@@ -1581,7 +1581,28 @@ public void commitAsync(final Map<TopicPartition,
OffsetAndMetadata> offsets, Of
* Overrides the fetch offsets that the consumer will use on the next
{@link #poll(Duration) poll(timeout)}. If this API
* is invoked for the same partition more than once, the latest offset
will be used on the next poll(). Note that
* you may lose data if this API is arbitrarily used in the middle of
consumption, to reset the fetch offsets
+ * <p>
+ * The next Consumer Record which will be retrieved when poll() is invoked
will have the offset specified, given that
+ * a record with that offset exists (i.e. it is a valid offset).
+ * <p>
+ * {@link #seekToBeginning(Collection)} will go to the first offset in the
topic.
+ * seek(0) is equivalent to seekToBeginning for a TopicPartition with
beginning offset 0,
+ * assuming that there is a record at offset 0 still available.
+ * {@link #seekToEnd(Collection)} is equivalent to seeking to the last
offset of the partition, but behavior depends on
+ * {@code isolation.level}, so see {@link #seekToBeginning(Collection)}
documentation for more details.
+ * <p>
+ * Seeking to the offset smaller than the log start offset or larger than
the log end offset
+ * or high watermark means an invalid offset is reached.
+ * Invalid offset behaviour is controlled by the {@link ConsumerConfig
AUTO_RESET_CONFIG} property.
+ * If this is set to "earliest", the next poll will return records from
the starting offset.
+ * If it is set to "latest", it will seek to the last offset (similar to
seekToEnd()).
+ * If it is set to "none", an {@code OffsetOutOfRangeException} will be
thrown.
+ * <p>
+ * Note that, the seek offset won't change to the in-flight fetch request,
it will take effect in next fetch request.
+ * So, the consumer might wait for {@code fetch.max.wait.ms} before
starting to fetch the records from desired offset.
*
+ * @param partition The TopicPartition on which the seek will be performed.
+ * @param offset the next offset returned by poll() will be either this or
greater.
Review Comment:
the main point is if you seek to offset 5, you'll also get offset 5 back (as
opposed to the next message being 6)
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