[GitHub] [rocketmq] ShannonDing opened a new issue, #5663: Messages may be lost when SyncStateSet expand in extreme scenarios

Wed, 07 Dec 2022 03:58:56 -0800 


ShannonDing opened a new issue, #5663:
URL: https://github.com/apache/rocketmq/issues/5663

   **BUG REPORT**
   
   1. Please describe the issue you observed:
   
   - What did you do (The steps to reproduce)?
   
   当前 SyncStateSet 变更的时候，由Master 
Broker上报并且Controller成功应用后才会应用到本地，这保证了SyncStateSet收缩时不会有消息丢失。但是这无法保证SyncStateSet扩张时数据的一致性性，举一个例子
   
   A为Master，B为Slave，一开始SyncStatetSet为{A}，当B追上A时（slaveAckOffset > 
confirmOffset）, 
SyncStateSet将从{A}变成{A,B}，按照当前实现的逻辑，首先{A,B}要上报Controller成功应用后才会应用到本地，因此在上报Controller到Controller确认应用成功这段时间内，SyncStateSet仍然为{A}，此时发送过来的消息只需要A确认即可返回成功，假设Controller成功应用上报的信息SyncStateSet为{A，B}，但返回给A确认丢失，此时A下线，由于Controller中SyncStateSet为{A,B}，B被选为主，那么就可能会出现消息丢失。
   
   
![image](https://user-images.githubusercontent.com/16487356/206173740-124073e5-4d64-4c3f-abee-77df6301b568.png)
   
   
   
   - What is expected to see?
   
   - What did you see instead?
   
   2. Please tell us about your environment:
   
   3. Other information (e.g. detailed explanation, logs, related issues, 
suggestions on how to fix, etc):


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