[GitHub] [hadoop] ZanderXu commented on pull request #4219: HDFS-16557. BootstrapStandby failed because of checking gap for inprogress EditLogInputStream

[GitBox <gi...@apache.org>]

ZanderXu commented on PR #4219:
URL: https://github.com/apache/hadoop/pull/4219#issuecomment-1150668804

   Thanks @tomscut , after tracing the code, I think we cannot add `elis.isInProgress()`.
   
   And I will explain my ideas trough questions and answers. 
   **Question one: Why was INVALID_TXID considered in the original code?**
   - CheckForGaps method is used to check whether streams contains continuous TXids from fromTxId to toAtLeastTxid
   - LastTxId equals INVALID_TXID means the stream is in progress
   - toAtLeastTxid maybe abnormal value, like Long.MaxValue.  So the CheckForGaps method only need to cover the latest inprogress segment.
   
   **Question two: What is the difference between INVALID_TXID and is InProgress()？**
   - Before introducing [SBN READ], LastTxId equals INVALID_TXID means the stream is in progress. And stream is in progress means it's lastTxId is INVALID_TXID.
   - But after introducing [SBN READ], LastTxId equals INVALID_TXID means the stream is in progress. But stream is in progress cannot mean it's lastTxId is INVALID_TXID. Because introducing getJournaledEdits.
   - So if we add `elis.isInProgress()` in CheckForGaps, it cannot cover the last writing segments which actual contains latest edit.
   
   Please correct me if anything is wrong.
   
   
   


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