read-only access to existing tables for speculative execution
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Key: ACCUMULO-132
URL: https://issues.apache.org/jira/browse/ACCUMULO-132
Project: Accumulo
Issue Type: New Feature
Components: client
Affects Versions: 1.5.0
Reporter: Eric Newton
Assignee: Eric Newton
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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