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From "Srikanth Kakani (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2247) Mappers fail easily due to repeated failures
Date Thu, 22 Nov 2007 00:58:43 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12544666
] 

Srikanth Kakani commented on HADOOP-2247:
-----------------------------------------

I think you are right 15 retries are being done but 5 of them fail in a bunch, really as one
failure. Backoff should help in that. However the cluster size should also play a part as
there will be lot more fetches and hence higher probability of failure. A ratio would help
in considering that aspect. There may be better metrics for that.

> 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
>
> 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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