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https://issues.apache.org/jira/browse/HADOOP-1158?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12501870
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Arun C Murthy edited comment on HADOOP-1158 at 6/6/07 8:27 PM:
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bq.b) Given sufficient fetch-failures per-map (say 3 or 4), the reducer then
complains to the JobTracker via a new rpc:
I take that back.. I propose we augument TaskStatus itself to let the
JobTracker know about the failed-fetches i.e. map taskids.
We could just add an new RPC to TaskUmbilicalProtocol for the reduce-task to
let the TaskTracker know about the failed fetch...
{code:title=TaskUmbilical.java}
void fetchError(String taskId, String failedFetchMapTaskId);
{code}
Even better, a tad more involved, is to rework
{code:title=TaskUmbilical.java}
void progress(String taskid, float progress, String state,
TaskStatus.Phase phase, Counters counters)
throws IOException, InterruptedException;
{code}
as
{code:title=TaskUmbilical.java}
void progress(String taskid, TaskStatus taskStatus}
throws IOException, InterruptedException;
{code}
This simplies the flow so that the child-vm itself computes it's {{TaskStatus}}
(which will be augumented to contain the failed-fetch-mapIds) and sends it
along the {{TaskTracker}} which just forwards it to the {{JobTracker}}, thereby
relieving it of some of the responsibilities vis-a-vis computing the
{{TaskStatus}}. Clearly this could be linked to the the reporting re-design at
HADOOP-1462 ...
Thoughts?
was:
bq.b) Given sufficient fetch-failures per-map (say 3 or 4), the reducer then
complains to the JobTracker via a new rpc:
I take that back, I'm propose we use augument TaskStatus itself to let the
JobTracker know about the failed-fetches i.e. map taskids, we could just add an
new RPC to TaskUmbilicalProtocol for the reduce-task to let the TaskTracker
know about the failed fetch.
> JobTracker should collect statistics of failed map output fetches, and take
> decisions to reexecute map tasks and/or restart the (possibly faulty) Jetty
> server on the TaskTracker
> ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-1158
> URL: https://issues.apache.org/jira/browse/HADOOP-1158
> Project: Hadoop
> Issue Type: Improvement
> Components: mapred
> Affects Versions: 0.12.2
> Reporter: Devaraj Das
> Assignee: Arun C Murthy
>
> The JobTracker should keep a track (with feedback from Reducers) of how many
> times a fetch for a particular map output failed. If this exceeds a certain
> threshold, then that map should be declared as lost, and should be reexecuted
> elsewhere. Based on the number of such complaints from Reducers, the
> JobTracker can blacklist the TaskTracker. This will make the framework
> reliable - it will take care of (faulty) TaskTrackers that sometimes always
> fail to serve up map outputs (for which exceptions are not properly
> raised/handled, for e.g., if the exception/problem happens in the Jetty
> server).
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