[HDFS-3883] DFSClient NPE due to missing block when opening a file

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 1.0.0
• Component/s: hdfs-client
• Target Version/s: 1.3.0
• Assignee: Eli Collins
• Reporter: Eli Collins
• Created: 01/Sep/12 01:43
• Updated: 14/May/13 05:12

Description

I saw the following NPE for a client on branch-1 that looks like it accessed a block not in the volume map, probably because the block was already deleted (otherwise the primary should have a block file). Looks like a create is racing with a delete.

DFSClient.java in updateBlockInfo..

Block newBlock = primary.getBlockInfo(last.getBlock());
long newBlockSize = newBlock.getNumBytes();    <--------

From getBlockInfo to getStoredBlock..

  public synchronized Block getStoredBlock(long blkid) throws IOException {
    File blockfile = findBlockFile(blkid);
    if (blockfile == null) {
      return null;
    }

Digging into findBlockFile..

  public synchronized File findBlockFile(long blockId) {
    final Block b = new Block(blockId);
    File blockfile = null;
    ActiveFile activefile = ongoingCreates.get(b);
    if (activefile != null) {
      blockfile = activefile.file;
    }
    if (blockfile == null) {
      blockfile = getFile(b);
    }
    if (blockfile == null) {
      if (DataNode.LOG.isDebugEnabled()) {
        DataNode.LOG.debug("ongoingCreates=" + ongoingCreates);
        DataNode.LOG.debug("volumeMap=" + volumeMap);
      }
    }
    return blockfile;

Into getFile..

  public synchronized File getFile(Block b) {
    DatanodeBlockInfo info = volumeMap.get(b);
    if (info != null) {
      return info.getFile();
    }
    return null;