From ab71c56973518bac8e1868eccdc40b17d7da35c1 Mon Sep 17 00:00:00 2001
From: Okada Haruki <ocadaruma@gmail.com>
Date: Fri, 14 Jul 2023 12:14:31 +0900
Subject: [PATCH] KAFKA-12261: Mention about potential delivery loss on
 increasing partition when auto.offset.reset = latest (#10167)

Splitting partitions while setting auto.offset.reset to latest may cause message delivery loss, but users might not be aware about that since currently it isn't documented anywhere.

Reviewers: Luke Chen <showuon@gmail.com>
---
 .../apache/kafka/clients/consumer/ConsumerConfig.java    | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java b/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java
index ec94748221b..6a56ba5a1cc 100644
--- a/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java
+++ b/clients/src/main/java/org/apache/kafka/clients/consumer/ConsumerConfig.java
@@ -149,7 +149,14 @@ public class ConsumerConfig extends AbstractConfig {
      * <code>auto.offset.reset</code>
      */
     public static final String AUTO_OFFSET_RESET_CONFIG = "auto.offset.reset";
-    public static final String AUTO_OFFSET_RESET_DOC = "What to do when there is no initial offset in Kafka or if the current offset does not exist any more on the server (e.g. because that data has been deleted): <ul><li>earliest: automatically reset the offset to the earliest offset<li>latest: automatically reset the offset to the latest offset</li><li>none: throw exception to the consumer if no previous offset is found for the consumer's group</li><li>anything else: throw exception to the consumer.</li></ul>";
+    public static final String AUTO_OFFSET_RESET_DOC = "What to do when there is no initial offset in Kafka or if the current offset does not exist any more on the server " +
+            "(e.g. because that data has been deleted): " +
+            "<ul><li>earliest: automatically reset the offset to the earliest offset" +
+            "<li>latest: automatically reset the offset to the latest offset</li>" +
+            "<li>none: throw exception to the consumer if no previous offset is found for the consumer's group</li>" +
+            "<li>anything else: throw exception to the consumer.</li></ul>" +
+            "<p>Note that altering partition numbers while setting this config to latest may cause message delivery loss since " +
+            "producers could start to send messages to newly added partitions (i.e. no initial offsets exist yet) before consumers reset their offsets.";
 
     /**
      * <code>fetch.min.bytes</code>