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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7359) Pluggable interface for cluster membership
Date Mon, 04 Jul 2011 11:52:22 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7359?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13059399#comment-13059399

Steve Loughran commented on HADOOP-7359:

Some more comments after looking at the code

* It'd be good to split cleanup (imports, better iteration) from the cluster changes, and
put the cleanup in first.
* I'm not sure about logging excludes data at info level; it seems over-verbose. If it does
go in, it should link to a wiki page on ExcludesFile to say "don't panic, this is optional"
* Following on with the new API model, I think the clustering should be a class, not an interface
* There's an assumption in the code that get[Excluded]Hosts() never fails; probably an implicit
one that it's fast. It'd make sense for the calls to be able to throw IOEs, as they could
be triggering live directory lookups, and if bounded execution time is a requirement, that
should be in the javadocs "must return in under 100 milliseconds"
* I wouldn't mark the various AdminOperationsProtocols as stable, as they are clearly moving

Related to this, I could imagine another JIRA issue of a kill -something that would trigger
a refresh on any/all registered services in the VM. That way even if you don't have a refresh
rate, you can manually trigger a reload. 

> Pluggable interface for cluster membership
> ------------------------------------------
>                 Key: HADOOP-7359
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7359
>             Project: Hadoop Common
>          Issue Type: Improvement
>            Reporter: Travis Crawford
>         Attachments: HADOOP-7359.diff
> Currently Hadoop uses local files to determine cluster membership. With HDFS for example,
dfs.hosts and dfs.hosts.exclude are used.
> To enable tighter integrations cluster membership should be an interface, with the current
file-based functionality provided as the default implementation. The common case would be
no functional change, however, sites could plug an alternative implementation in, such as
pulling the machine lists from a machine database.
> Two machine lists, includes and excludes, are used to define cluster membership and state.
HostsFileReader currently handles reading these lists from files, who's names are passed in
by FSNamesystem for HDFS and JobTracker for MR.
> The proposed change is adding a HostsReader interface to common, and changing HostsFileReader
to an abstract class that functions the same as today.
> Two new classes, DFSHostsFileReader and MRHostsFileReader, extend HostsFileReader and
simply pass the appropriate file names in. These new classes are needed because config key
names live outside common.
> Two new conf keys, defaulting to the file-based readers, would be added to choose a different
hosts reader: dfs.namenode.hosts.reader.class mapreduce.jobtracker.hosts.reader.class
> Comments/suggestions? I have most of this written already but would love some feedback
on the general idea before posting the diff.

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