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https://issues.apache.org/jira/browse/HADOOP-2247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12551686
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Amar Kamat commented on HADOOP-2247:
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- {{duration-before-stall}} is computed as
{{shuffle-start-time - last-successful-map-output-copy-time}}. In most of the
cases {{duration-before-stall}} should dominate but we also consider
{{max-map-completion-time}} as to make sure that we wait at least
{{max-map-completion-time}} amount of time and not kill the reducer to before
that.
- {{/2}} is just a measure to distinguish between the cases where the reducer
has developed some faults and network/jetty congestions.
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Comments? Any better measures? Any strong opinions on the usage of {{max}} or
{{+}} operator in the {{min-shuffle-exec}} computation?
> Mappers fail easily due to repeated failures
> --------------------------------------------
>
> Key: HADOOP-2247
> URL: https://issues.apache.org/jira/browse/HADOOP-2247
> Project: Hadoop
> Issue Type: Bug
> Affects Versions: 0.15.0
> Environment: 1400 Node hadoop cluster
> Reporter: Srikanth Kakani
> Assignee: Amar Kamat
> Priority: Blocker
> Fix For: 0.15.2
>
> Attachments: HADOOP-2220.patch, HADOOP-2220.patch
>
>
> Related to HADOOP-2220, problem introduced in HADOOP-1158
> At this scale hardcoding the number of fetch failures to a static number: in
> this case 3 is never going to work. Although the jobs we are running are
> loading the systems 3 failures can randomly occur within the lifetime of a
> map. Even fetching the data can cause enough load for so many failures to
> occur.
> We believe that number of tasks and size of cluster should be taken into
> account. Based on which we believe that a ratio between total fetch attempts
> and total failed attempts should be taken into consideration.
> Given our experience with a task should be declared "Too many fetch failures"
> based on:
> failures > n /*could be 3*/ && (failures/total attempts) > k% /*could be
> 30-40%*/
> Basically the first factor is to give some headstart to the second factor,
> second factor then takes into account the cluster size and the task size.
> Additionally we could take recency into account, say failures and attempts in
> last one hour. We do not want to make it too small.
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