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From "Brahma Reddy Battula (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-6489) DFS Used space is not correct computed on frequent append operations
Date Wed, 09 Aug 2017 12:23:01 GMT

    [ https://issues.apache.org/jira/browse/HDFS-6489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16119797#comment-16119797
] 

Brahma Reddy Battula commented on HDFS-6489:
--------------------------------------------

bq.Even with this, dfsUsed and numblocks counting is all messed up. e.g. FsDatasetImpl.removeOldBlock
calls decDfsUsedAndNumBlocks twice (so even though dfsUsed is correctly decremented, numBlocks
is not)
Nope. I believe you read this wrong.
{{FsDatasetImpl#removeOldReplica}} call two seperate calls {{onBlockFileDeletion(..)}} and
{{onMetaFileDeletion(...)}} for {{blockfile}} and {{metafile}} respectively.
{code}
    // Remove the old replicas
    if (replicaInfo.deleteBlockData() || !replicaInfo.blockDataExists()) {
      FsVolumeImpl volume = (FsVolumeImpl) replicaInfo.getVolume();
      volume.onBlockFileDeletion(bpid, replicaInfo.getBytesOnDisk());
      if (replicaInfo.deleteMetadata() || !replicaInfo.metadataExists()) {
        volume.onMetaFileDeletion(bpid, replicaInfo.getMetadataLength());
      }
{code}

 *Code from {{FsVolumeImpl.java}}* 
{code}
 void onBlockFileDeletion(String bpid, long value) {
    decDfsUsedAndNumBlocks(bpid, value, true);
    if (isTransientStorage()) {
      dataset.releaseLockedMemory(value, true);
    }
  }

  void onMetaFileDeletion(String bpid, long value) {
    decDfsUsedAndNumBlocks(bpid, value, false);
  }

  private void decDfsUsedAndNumBlocks(String bpid, long value,
                                      boolean blockFileDeleted) {
    try(AutoCloseableLock lock = dataset.acquireDatasetLock()) {
      BlockPoolSlice bp = bpSlices.get(bpid);
      if (bp != null) {
        bp.decDfsUsed(value);
        if (blockFileDeleted) {
          bp.decrNumBlocks();
        }
      }
    }
  }
{code}

{{onBlockFileDeletion(..)}} calls {{decDfsUsedAndNumBlocks(bpid, value, true);}} with {{blockFileDeleted}}
flag as {{true}} to drement the {{numblocks}},where as   {{onMetaFileDeletion(...)}} calls
{{decDfsUsedAndNumBlocks(bpid, value, false);}} with {{blockFileDeleted}} flag as {{false}}.Because,no
need to decrement the {{numblocks}} for metafile deletion.


bq.Also, what do you think about a robust unit-test framework to find out all these issues?

Only way is to list all write/delete cases and write tests for that

 *Comments for this Jira* 

1) only {{incDfsUsed()}} should be used, as {{numBlocks}} will be updated during {{createRbw()}}
for new blocks. For {{append}} incrementing {{numBlocks}} not required.
2) Previous metadata length also should be deducted.
{code}
860	    if(b instanceof ReplicaInfo) {
861	      ReplicaInfo replicaInfo  = ((ReplicaInfo) b);
862	      if(replicaInfo.getState() == ReplicaState.RBW) {
863	        ReplicaInPipeline rip = (ReplicaInPipeline) replicaInfo;
864	        // rip.getOriginalBytesReserved() - rip.getBytesReserved()
865	        // is the amount of data that was written to the replica
866	        long bytesAdded = rip.getOriginalBytesReserved() -
867	        rip.getBytesReserved() + replicaInfo.getMetaFile().length();
868	        incDfsUsedAndNumBlocks(bpid, bytesAdded);
869	      }
870	    }
{code}

Sorry for late reply.

> DFS Used space is not correct computed on frequent append operations
> --------------------------------------------------------------------
>
>                 Key: HDFS-6489
>                 URL: https://issues.apache.org/jira/browse/HDFS-6489
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>    Affects Versions: 2.2.0, 2.7.1, 2.7.2
>            Reporter: stanley shi
>            Assignee: Weiwei Yang
>         Attachments: HDFS-6489.001.patch, HDFS-6489.002.patch, HDFS-6489.003.patch, HDFS-6489.004.patch,
HDFS-6489.005.patch, HDFS-6489.006.patch, HDFS-6489.007.patch, HDFS6489.java
>
>
> The current implementation of the Datanode will increase the DFS used space on each block
write operation. This is correct in most scenario (create new file), but sometimes it will
behave in-correct(append small data to a large block).
> For example, I have a file with only one block(say, 60M). Then I try to append to it
very frequently but each time I append only 10 bytes;
> Then on each append, dfs used will be increased with the length of the block(60M), not
teh actual data length(10bytes).
> Consider in a scenario I use many clients to append concurrently to a large number of
files (1000+), assume the block size is 32M (half of the default value), then the dfs used
will be increased 1000*32M = 32G on each append to the files; but actually I only write 10K
bytes; this will cause the datanode to report in-sufficient disk space on data write.
> {quote}2014-06-04 15:27:34,719 INFO org.apache.hadoop.hdfs.server.datanode.DataNode:
opWriteBlock  BP-1649188734-10.37.7.142-1398844098971:blk_1073742834_45306 received exception
org.apache.hadoop.util.DiskChecker$DiskOutOfSpaceException: Insufficient space for appending
to FinalizedReplica, blk_1073742834_45306, FINALIZED{quote}
> But the actual disk usage:
> {quote}
> [root@hdsh143 ~]# df -h
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda3              16G  2.9G   13G  20% /
> tmpfs                 1.9G   72K  1.9G   1% /dev/shm
> /dev/sda1              97M   32M   61M  35% /boot
> {quote}



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