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https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12558834#action_12558834
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Owen O'Malley commented on HADOOP-1985:
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I'm worried about the time and memory performance of this. Have you run a sort
with dfs cluster == map/reduce cluster and compared running times and job
tracker memory size? We've already seen cases where the current pollForNewTask
causes performance problems...
It bothers me that the max levels is hard coded rather than configurable.
>From a style point of view, I probably would have defined a new class rather
>than use nested java.utils containers like List<Map<Node,
>List<TaskInProgress>>>. That way if we change the representation later it
>won't be scattered through the code. In particular, I can imagine wanting to
>have the data structure be something like:
Map<String (rack name), RackInfo> and RackInfo has a Map<String (hostname),
List<TaskInProgress> >. Or even more tree-like...
Did you need to change the definition of findNewTask? I don't see it in the
patch.
This needs user documentation in forrest.
The java doc on DNSToSwitchMapping.resolve should probably mention that they
must cache if their operation is expensive. Although there isn't a way to clear
or update that cache, which might be a problem at some point...
You don't really need the Scan example, you could use the
GenericMRLoadGenerator with a -keepmap of 0.
In the longer term I think a configured mapping class would be useful. A class
named
org.apache.hadoop.net.ConfiguredNodeMapping that let you set the mapping in
your config. Something like:
{code}
<property>
<name>hadoop.configured.node.mapping</name>
<value>host1=/rack1,host2=/rack1,host3=/rack4</value>
</property>
> Abstract node to switch mapping into a topology service class used by
> namenode and jobtracker
> ---------------------------------------------------------------------------------------------
>
> Key: HADOOP-1985
> URL: https://issues.apache.org/jira/browse/HADOOP-1985
> Project: Hadoop
> Issue Type: New Feature
> Components: dfs, mapred
> Reporter: eric baldeschwieler
> Assignee: Devaraj Das
> Fix For: 0.16.0
>
> Attachments: 1985.new.patch, 1985.v1.patch, 1985.v2.patch,
> 1985.v3.patch, 1985.v4.patch, 1985.v5.patch, 1985.v6.patch
>
>
> In order to implement switch locality in MapReduce, we need to have switch
> location in both the namenode and job tracker. Currently the namenode asks
> the data nodes for this info and they run a local script to answer this
> question. In our environment and others that I know of there is no reason to
> push this to each node. It is easier to maintain a centralized script that
> maps node DNS names to switch strings.
> I propose that we build a new class that caches known DNS name to switch
> mappings and invokes a loadable class or a configurable system call to
> resolve unknown DNS to switch mappings. We can then add this to the namenode
> to support the current block to switch mapping needs and simplify the data
> nodes. We can also add this same callout to the job tracker and then
> implement rack locality logic there without needing to chane the filesystem
> API or the split planning API.
> Not only is this the least intrusive path to building racklocal MR I can ID,
> it is also future compatible to future infrastructures that may derive
> topology on the fly, etc, etc...
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