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https://issues.apache.org/jira/browse/HDFS-17049?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17732801#comment-17732801
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ASF GitHub Bot commented on HDFS-17049:
---------------------------------------

umamaheswararao commented on PR #5743:
URL: https://github.com/apache/hadoop/pull/5743#issuecomment-1592121456

   Quite surprised to see how this can happen, we have write lock while getting 
nextBlockID
   
   ```
   private long nextBlockId(BlockType blockType) throws IOException {
     assert hasWriteLock();
     checkNameNodeSafeMode(“Cannot get next block ID”);
     final long blockId = blockManager.nextBlockId(blockType);
     getEditLog().logAllocateBlockId(blockId);
   ```




> EC: Fix duplicate block group IDs generated by SequentialBlockGroupIdGenerator
> ------------------------------------------------------------------------------
>
>                 Key: HDFS-17049
>                 URL: https://issues.apache.org/jira/browse/HDFS-17049
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Shuyan Zhang
>            Assignee: Shuyan Zhang
>            Priority: Major
>              Labels: pull-request-available
>
> When I used multiple clients to write EC files concurrently, I found that 
> NameNode generated the same block group ID for different files:
> ```
> 2023-06-13 20:09:59,514 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* 
> allocate blk_-9223372036854697568_14389 for /ec-test/10/4068034329705654124
> 2023-06-13 20:09:59,514 INFO org.apache.hadoop.hdfs.StateChange: BLOCK* 
> allocate blk_-9223372036854697568_14390 for /ec-test/19/7042966144171770731
> ```
> After diving into `SequentialBlockGroupIdGenerator`, I found that the current 
> implementation of `nextValue` is not thread-safe.
> This problem must be fixed.



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