[jira] [Created] (HDFS-2492) BlockManager cross-rack replication checks only work for ScriptBasedMapping

["Steve Loughran (Created) (JIRA)" <ji...@apache.org>]

BlockManager cross-rack replication checks only work for ScriptBasedMapping
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                 Key: HDFS-2492
                 URL: https://issues.apache.org/jira/browse/HDFS-2492
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 0.23.0, 0.24.0
            Reporter: Steve Loughran


The BlockManager cross-rack replication checks only works if script files are used for replication, not if alternate plugins provide the topology information.

This is because the BlockManager sets its rack checking flag if there is a filename key
{code}
shouldCheckForEnoughRacks = conf.get(DFSConfigKeys.NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY) != null;
{code}
yet this filename key is only used if the topology mapper defined by 
{code}
DFSConfigKeys.NET_TOPOLOGY_NODE_SWITCH_MAPPING_IMPL_KEY
{code}
is an instance of {{ScriptBasedMapping}}

If any other mapper is used, the system may be multi rack, but the Block Manager will not be aware of this fact unless the filename key is set to something non-null

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