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From "Sean Busbey (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-132) read-only access to existing tables for speculative execution
Date Mon, 21 Apr 2014 05:28:20 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13975408#comment-13975408
] 

Sean Busbey commented on ACCUMULO-132:
--------------------------------------

This reads like it's OBE from the offline mode for our InputFormats.

> read-only access to existing tables for speculative execution
> -------------------------------------------------------------
>
>                 Key: ACCUMULO-132
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-132
>             Project: Accumulo
>          Issue Type: New Feature
>          Components: client
>            Reporter: Eric Newton
>            Priority: Minor
>
> An accumulo user has a need to perform a map/reduce over an entire table.   Right now,
if a tablet server is running on a machine that has become slow due to failing hardware (it
happens... a lot), the mapper using that server also runs slowly.  If we allow speculative
execution, the second map just goes back to the same tablet server, doubling the load on our
already slow server.  However, the data behind the tablet server is sitting there in multiple
locations in HDFS.  The user can live without pulling the most recent updates in the tablet
server's memory.
> Possible solutions:
>  # provide read-only hosting of a tablet from another node, possibly on demand
>  # convenient way of re-creating the tablet server iterator stack and reading the files
directly
>  # clone the table/tablet (has the benefit that a reference is maintained in the metadata
table)



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