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https://issues.apache.org/jira/browse/HADOOP-1985?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Allen Wittenauer updated HADOOP-1985:
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Release Note:
This issue introduces rack awareness for map tasks. It also moves the rack
resolution logic to the central servers - NameNode & JobTracker. The
administrator can specify a loadable class given by
topology.node.switch.mapping.impl to specify the class implementing the logic
for rack resolution. The class must implement a method - resolve(List<String>
names), where names is the list of DNS-names/IP-addresses that we want
resolved. The return value is a list of resolved network paths of the form
/foo/rack, where rack is the rackID where the node belongs to and foo is the
switch where multiple racks are connected, and so on. The default
implementation of this class is packaged along with hadoop and points to
org.apache.hadoop.net.ScriptBasedMapping and this class loads a script that can
be used for rack resolution. The script location is configurable. It is
specified by topology.script.file.name and defaults to an empty script. In the
case where the script name is empty, /default-rack is returned for all
dns-names/IP-addresses. The loadable topology.node.switch.mapping.impl provides
administrators fleixibilty to define how their site's node resolution should
happen.
For mapred, one can also specify the level of the cache w.r.t the number of
levels in the resolved network path - defaults to two. This means that the
JobTracker will cache tasks at the host level and at the rack level.
Known issue: the task caching will not work with levels greater than 2 (beyond
racks). This bug is tracked in HADOOP-3296.
was:
This issue introduces rack awareness for map tasks. It also moves the rack
resolution logic to the central servers - NameNode & JobTracker. The
administrator can specify a loadable class given by
topology.node.switch.mapping.impl to specify the class implementing the logic
for rack resolution. The class must implement a method - resolve(List\<String\>
names), where names is the list of DNS-names/IP-addresses that we want
resolved. The return value is a list of resolved network paths of the form
/foo/rack, where rack is the rackID where the node belongs to and foo is the
switch where multiple racks are connected, and so on. The default
implementation of this class is packaged along with hadoop and points to
org.apache.hadoop.net.ScriptBasedMapping and this class loads a script that can
be used for rack resolution. The script location is configurable. It is
specified by topology.script.file.name and defaults to an empty script. In the
case where the script name is empty, /default-rack is returned for all
dns-names/IP-addresses. The loadable topology.node.switch.mapping.impl provides
administrators fleixibilty to define how their site's node resolution should
happen.
For mapred, one can also specify the level of the cache w.r.t the number of
levels in the resolved network path - defaults to two. This means that the
JobTracker will cache tasks at the host level and at the rack level.
Known issue: the task caching will not work with levels greater than 2 (beyond
racks). This bug is tracked in HADOOP-3296.
> 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 Common
> Issue Type: New Feature
> Reporter: eric baldeschwieler
> Assignee: Devaraj Das
> Fix For: 0.17.0
>
> Attachments: 1985.new.patch, 1985.v1.patch, 1985.v10.patch,
> 1985.v11.patch, 1985.v19.patch, 1985.v2.patch, 1985.v20.patch,
> 1985.v23.patch, 1985.v24.patch, 1985.v25.patch, 1985.v3.patch, 1985.v4.patch,
> 1985.v5.patch, 1985.v6.patch, 1985.v9.patch, jobinprogress.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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