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https://issues.apache.org/jira/browse/SYSTEMML-1831?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Fei Hu updated SYSTEMML-1831:
-----------------------------
    Description: 
For the {{rangeReIndex}} operation, it needs to read the whole input matrix 
into memory first and do the subsetting in the memory. It is not efficient 
because it needs to read a lot of unnecessary data, and even will be out of 
memory if the size of input matrix exceeds the available memory. 

The plan here is to read the keys in the Hadoop sequence file, and identify the 
keys overlapped with the input range index. Then the values specified by the 
identified keys will be read.

  was:
For the {{rangeReIndex}} operation, it needs to read the whole input matrix 
into memory first and do the subsetting in the memory. It is not efficient 
because it needs to read a lot of unnecessary data, and even out of memory if 
the size of input matrix exceeds the available memory. 

The plan here is to read the keys in the Hadoop sequence file, and identify the 
keys overlapped with the input range index. Then the values specified by the 
identified keys will be read.


> Improve the efficiency of matrix subsetting
> -------------------------------------------
>
>                 Key: SYSTEMML-1831
>                 URL: https://issues.apache.org/jira/browse/SYSTEMML-1831
>             Project: SystemML
>          Issue Type: Improvement
>            Reporter: Fei Hu
>            Assignee: Fei Hu
>
> For the {{rangeReIndex}} operation, it needs to read the whole input matrix 
> into memory first and do the subsetting in the memory. It is not efficient 
> because it needs to read a lot of unnecessary data, and even will be out of 
> memory if the size of input matrix exceeds the available memory. 
> The plan here is to read the keys in the Hadoop sequence file, and identify 
> the keys overlapped with the input range index. Then the values specified by 
> the identified keys will be read.



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