[jira] [Commented] (HDFS-2798) Append may race with datanode block scanner, causing replica to be incorrectly marked corrupt

["Todd Lipcon (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-2798?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13187170#comment-13187170 ] 

Todd Lipcon commented on HDFS-2798:
-----------------------------------

You can reproduce this fairly reliably by adding a sleep call in BlockReceiver as follows:

{code}

        case PIPELINE_SETUP_APPEND:
          replicaInfo = datanode.data.append(block, newGs, minBytesRcvd);
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
          }
          if (datanode.blockScanner != null) { // remove from block scanner
            datanode.blockScanner.deleteBlock(block.getBlockPoolId(),
                block.getLocalBlock());
          }
          block.setGenerationStamp(newGs);
          break;
{code}
TestFileAppend2 will then time out.
                
> Append may race with datanode block scanner, causing replica to be incorrectly marked corrupt
> ---------------------------------------------------------------------------------------------
>
>                 Key: HDFS-2798
>                 URL: https://issues.apache.org/jira/browse/HDFS-2798
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: data-node
>    Affects Versions: 0.22.0, 0.23.0
>            Reporter: Todd Lipcon
>            Priority: Critical
>
> When a pipeline is setup for append, the block's metadata file is renamed before the block is removed from the datanode block scanner queues. This can cause a race condition where the block scanner incorrectly marks the block as corrupt, since it tries to scan the file corresponding to the old genstamp.
> This causes TestFileAppend2 to time out in extremely rare circumstances - the corrupt replica prevents the writer thread from completing the file.

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