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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3222) DFSInputStream#openInfo should not silently get the length as 0 when locations length is zero for last partial block.
Date Mon, 09 Apr 2012 16:45:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3222?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13249939#comment-13249939
] 

Todd Lipcon commented on HDFS-3222:
-----------------------------------

bq. I think our proposal won't work here, because by the time of hsync, DN will not report
to NN anyway.

On the first hflush() for a block, it calls NN.fsync(), which internally calls persistBlocks().
Currently, the fsync call doesn't give a length, but perhaps it could?

The other thought is that, after a restart, a block that was previously being written would
be in the under construction state, but with no expectedTargets. This differs from the case
where a block has been allocated but not yet written to replicas. We could use that to set
a new flag in the LocatedBlock response indicating that it's not a 0-length, but instead that
it's corrupt.

                
> DFSInputStream#openInfo should not silently get the length as 0 when locations length
is zero for last partial block.
> ---------------------------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-3222
>                 URL: https://issues.apache.org/jira/browse/HDFS-3222
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs client
>    Affects Versions: 1.0.3, 2.0.0, 3.0.0
>            Reporter: Uma Maheswara Rao G
>            Assignee: Uma Maheswara Rao G
>         Attachments: HDFS-3222-Test.patch
>
>
> I have seen one situation with Hbase cluster.
> Scenario is as follows:
> 1)1.5 blocks has been written and synced.
> 2)Suddenly cluster has been restarted.
> Reader opened the file and trying to get the length., By this time partial block contained
DNs are not reported to NN. So, locations for this partial block would be 0. In this case,
DFSInputStream assumes that, 1 block size as final size.
> But reader also assuming that, 1 block size is the final length and setting his end marker.
Finally reader ending up reading only partial data. Due to this, HMaster could not replay
the complete edits. 
> Actually this happend with 20 version. Looking at the code, same should present in trunk
as well.
> {code}
>     int replicaNotFoundCount = locatedblock.getLocations().length;
>     
>     for(DatanodeInfo datanode : locatedblock.getLocations()) {
> ..........
> ..........
>  // Namenode told us about these locations, but none know about the replica
>     // means that we hit the race between pipeline creation start and end.
>     // we require all 3 because some other exception could have happened
>     // on a DN that has it.  we want to report that error
>     if (replicaNotFoundCount == 0) {
>       return 0;
>     }
> {code}

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