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  1. Hadoop HDFS
  2. HDFS-15240

Erasure Coding: dirty buffer causes reconstruction block error

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      1. When read some lzo files we found some blocks were broken.

      I read back all internal blocks(b0-b8) of the block group(RS-6-3-1024k) from DN directly, and choose 6(b0-b5) blocks to decode other 3(b6', b7', b8') blocks. And find the longest common sequenece(LCS) between b6'(decoded) and b6(read from DN)(b7'/b7 and b8'/b8).

      After selecting 6 blocks of the block group in combinations one time and iterating through all cases, I find one case that the length of LCS is the block length - 64KB, 64KB is just the length of ByteBuffer used by StripedBlockReader. So the corrupt reconstruction block is made by a dirty buffer.

      The following log snippet(only show 2 of 28 cases) is my check program output. In my case, I known the 3th block is corrupt, so need other 5 blocks to decode another 3 blocks, then find the 1th block's LCS substring is block length - 64kb.

      It means (0,1,2,4,5,6)th blocks were used to reconstruct 3th block, and the dirty buffer was used before read the 1th block.

      Must be noted that StripedBlockReader read from the offset 0 of the 1th block after used the dirty buffer.

      EDITED for readability.

      decode from block[0, 2, 3, 4, 5, 7] to generate block[1', 6', 8']
      Check the first 131072 bytes between block[1] and block[1'], the longest common substring length is 4
      Check the first 131072 bytes between block[6] and block[6'], the longest common substring length is 4
      Check the first 131072 bytes between block[8] and block[8'], the longest common substring length is 4
      decode from block[0, 2, 3, 4, 5, 6] to generate block[1', 7', 8']
      Check the first 131072 bytes between block[1] and block[1'], the longest common substring length is 65536
      CHECK AGAIN: all 27262976 bytes between block[1] and block[1'], the longest common substring length is 27197440  # this one
      Check the first 131072 bytes between block[7] and block[7'], the longest common substring length is 4
      Check the first 131072 bytes between block[8] and block[8'], the longest common substring length is 4

      Now I know the dirty buffer causes reconstruction block error, but how does the dirty buffer come about?

      After digging into the code and DN log, I found this following DN log is the root reason.

      [INFO] [stripedRead-1017] : Interrupted while waiting for IO on channel java.nio.channels.SocketChannel[connected local=/xxxxxxxx:52586 remote=/xxxxxxxx:50010]. 180000 millis timeout left.
      [WARN] [StripedBlockReconstruction-199] : Failed to reconstruct striped block: BP-714356632-xxxxxxxx-1519726836856:blk_-YYYYYYYYYYYYYY_3472979393
      java.lang.NullPointerException
          at org.apache.hadoop.hdfs.util.StripedBlockUtil.getNextCompletedStripedRead(StripedBlockUtil.java:314)
          at org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.doReadMinimumSources(StripedReader.java:308)
          at org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedReader.readMinimumSources(StripedReader.java:269)
          at org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.reconstruct(StripedBlockReconstructor.java:94)
          at org.apache.hadoop.hdfs.server.datanode.erasurecode.StripedBlockReconstructor.run(StripedBlockReconstructor.java:60)
          at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
          at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
          at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
          at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
          at java.base/java.lang.Thread.run(Thread.java:834) 

      Reading from DN may timeout(hold by a future(F)) and output the INFO log, but the futures that contains the future(F)  is cleared, 

      return new StripingChunkReadResult(futures.remove(future),
          StripingChunkReadResult.CANCELLED); 

      futures.remove(future) cause NPE. So the EC reconstruction is failed. In the finally phase, the code snippet in getStripedReader().close() 

      reconstructor.freeBuffer(reader.getReadBuffer());
      reader.freeReadBuffer();
      reader.closeBlockReader(); 

      free buffer firstly, but the StripedBlockReader still holds the buffer and write it, that pollute the buffer of BufferPool.

        Attachments

        1. HDFS-15240.001.patch
          3 kB
          HuangTao
        2. HDFS-15240.002.patch
          16 kB
          HuangTao
        3. HDFS-15240.003.patch
          16 kB
          HuangTao
        4. HDFS-15240.004.patch
          17 kB
          HuangTao
        5. HDFS-15240.005.patch
          17 kB
          HuangTao
        6. HDFS-15240.006.patch
          17 kB
          HuangTao
        7. HDFS-15240.007.patch
          19 kB
          HuangTao
        8. HDFS-15240.008.patch
          19 kB
          HuangTao
        9. HDFS-15240.009.patch
          18 kB
          HuangTao
        10. HDFS-15240.010.patch
          19 kB
          HuangTao
        11. HDFS-15240.011.patch
          19 kB
          HuangTao
        12. HDFS-15240.012.patch
          19 kB
          HuangTao
        13. HDFS-15240.013.patch
          19 kB
          HuangTao
        14. HDFS-15240-branch-3.1.001.patch
          20 kB
          Hui Fei
        15. HDFS-15240-branch-3.1-001.patch
          20 kB
          HuangTao
        16. HDFS-15240-branch-3.2.001.patch
          19 kB
          Xiaoqiao He
        17. HDFS-15240-branch-3.3.001.patch
          19 kB
          Hui Fei
        18. HDFS-15240-branch-3.3-001.patch
          19 kB
          HuangTao
        19. image-2020-07-16-15-56-38-608.png
          551 kB
          Hongbing Wang
        20. org.apache.hadoop.hdfs.TestReconstructStripedFile.txt
          5 kB
          Toshihiko Uchida
        21. org.apache.hadoop.hdfs.TestReconstructStripedFile-output.txt
          24.48 MB
          Toshihiko Uchida
        22. test-HDFS-15240.006.patch
          14 kB
          Toshihiko Uchida

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            People

            • Assignee:
              marvelrock HuangTao
              Reporter:
              marvelrock HuangTao
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              Dates

              • Created:
                Updated:
                Resolved: