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Date: Thu, 15 Apr 2010 21:21:25 -0400 (EDT)
From: "Aaron Kimball (JIRA)" <jira@apache.org>
To: common-issues@hadoop.apache.org
Subject: [jira] Commented: (HADOOP-6708) New file format for very large
 records
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    [ https://issues.apache.org/jira/browse/HADOOP-6708?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12857635#action_12857635 ] 

Aaron Kimball commented on HADOOP-6708:
---------------------------------------

I'm not sure what you mean by this optimization. Can you please explain further?

What's the relationship between "blocks" and "chunks" in a TFile? It sounds like a record can span multiple chunks. Is a record fully contained in a block? If it compresses an 8 GB record down to, say, 2 GB, will that still require skipping chunk-wise through the compressed data?

I do plan on using compression. Given the very large record lengths I'm designing for, I expect that it's acceptable to compress each record individually. The current writeup doesn't propose how to handle compression elegantly. But I'm leaning toward writing out a table of compressed record lengths at the end of the file.

> New file format for very large records
> --------------------------------------
>
>                 Key: HADOOP-6708
>                 URL: https://issues.apache.org/jira/browse/HADOOP-6708
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: io
>            Reporter: Aaron Kimball
>            Assignee: Aaron Kimball
>         Attachments: lobfile.pdf
>
>
> A file format that handles multi-gigabyte records efficiently, with lazy disk access

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