[jira] [Commented] (HADOOP-12041) Implement another Reed-Solomon coder in pure Java

["Kai Zheng (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-12041?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15084503#comment-15084503 ] 

Kai Zheng commented on HADOOP-12041:
------------------------------------

Hi [~walter.k.su],

I'm going to update this. Would you help with this question? In GF256.init(), it's mainly to initialize {{theGfMulTab}}. What did you mean by "still possible GF256 be inited twice"? Thanks.

> Implement another Reed-Solomon coder in pure Java
> -------------------------------------------------
>
>                 Key: HADOOP-12041
>                 URL: https://issues.apache.org/jira/browse/HADOOP-12041
>             Project: Hadoop Common
>          Issue Type: Sub-task
>            Reporter: Kai Zheng
>            Assignee: Kai Zheng
>         Attachments: HADOOP-12041-v1.patch, HADOOP-12041-v2.patch, HADOOP-12041-v3.patch, HADOOP-12041-v4.patch
>
>
> Currently existing Java RS coders based on {{GaloisField}} implementation have some drawbacks or limitations:
> * The decoder computes not really erased units unnecessarily (HADOOP-11871);
> * The decoder requires parity units + data units order for the inputs in the decode API (HADOOP-12040);
> * Need to support or align with native erasure coders regarding concrete coding algorithms and matrix, so Java coders and native coders can be easily swapped in/out and transparent to HDFS (HADOOP-12010);
> * It's unnecessarily flexible but incurs some overhead, as HDFS erasure coding is totally a byte based data system, we don't need to consider other symbol size instead of 256.
> This desires to implement another  RS coder in pure Java, in addition to the existing {{GaliosField}} from HDFS-RAID. The new Java RS coder will be favored and used by default to resolve the related issues. The old HDFS-RAID originated coder will still be there for comparing, and converting old data from HDFS-RAID systems.



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