[jira] Commented: (HIVE-1343) add an interface in RCFile to support concatenation of two files without (de)compression

["Ning Zhang (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HIVE-1343?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12867557#action_12867557 ] 

Ning Zhang commented on HIVE-1343:
----------------------------------

Yongqiang this patch only exposes the FileInputReader to the client and the client has to merge the file locally. This won't be scalable. What we should do is to run this merge job as a map-only job so that it can be run in parallel.

Talked with Dhruba and he think it would be possible to make it a map-only job. The idea is to define a new RecordReader that does not do decompression and iterate over records. Instead it iterates over uncompressed blocks. 

> add an interface in RCFile to support concatenation of two files without (de)compression
> ----------------------------------------------------------------------------------------
>
>                 Key: HIVE-1343
>                 URL: https://issues.apache.org/jira/browse/HIVE-1343
>             Project: Hadoop Hive
>          Issue Type: New Feature
>    Affects Versions: 0.6.0
>            Reporter: Ning Zhang
>            Assignee: He Yongqiang
>             Fix For: 0.6.0
>
>         Attachments: HIVE-1343.1.patch
>
>
> If two files are concatenated, we need to read each record in these files and write them back to the destination file. The IO cost is mostly unavoidable due to the lack of append functionality in HDFS. However the CPU cost could be significantly reduced by avoiding compression and decompression of the files.
> The File Format layer should provide API that implement the block-level concatenation. 

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