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https://issues.apache.org/jira/browse/HDFS-2492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13138647#comment-13138647
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Steve Loughran commented on HDFS-2492:
--------------------------------------
HADOOP-7777 contains all the hadoop-common code to add a new predicate to the
switch mappers (via a base class and a query method that handles mappers that
are not subclasses of that); once that is in the change to block manager will
be trivial.
reviews of that patch would be welcome
> BlockManager cross-rack replication checks only work for ScriptBasedMapping
> ---------------------------------------------------------------------------
>
> 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
> Priority: Blocker
>
> 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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