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From "Jothi Padmanabhan (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3638) Cache the iFile index files in memory to reduce seeks during map output serving
Date Fri, 12 Sep 2008 06:23:44 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3638?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12630497#action_12630497
] 

Jothi Padmanabhan commented on HADOOP-3638:
-------------------------------------------

What would be a reasonable amount of memory that can be set aside for the Index Cache at the
Map side?

Each individual record is 24 bytes (3 longs)
Let num reducers = R
Let num map slots = S
Let total number of Spill Files = M

Total Number of Entries per Map task = M*R*24

For a *node*, that is running S Map tasks (slots) at a time, total memory consumed = S*M*R*24

If M = 100, S = 6, R = 100, then 
Total Memory Consumed ~= 1.4M  

I think 1.4M is a a very reasonable amount for the index cache, at the node level. 

So, do we need to worry about the memory limit at the map side at all? We could just LRU at
the task tracker level alone.

> Cache the iFile index files in memory to reduce seeks during map output serving
> -------------------------------------------------------------------------------
>
>                 Key: HADOOP-3638
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3638
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: mapred
>    Affects Versions: 0.17.0
>            Reporter: Devaraj Das
>            Assignee: Jothi Padmanabhan
>             Fix For: 0.19.0
>
>         Attachments: hadoop-3638-v1.patch, hadoop-3638-v2.patch
>
>
> The iFile index files can be cached in memory to reduce seeks during map output serving.

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