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From "eric baldeschwieler (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-54) SequenceFile should compress blocks, not individual entries
Date Tue, 25 Jul 2006 04:48:16 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-54?page=comments#action_12423229 ] 
            
eric baldeschwieler commented on HADOOP-54:
-------------------------------------------

The point is that you can carry object compressed data through the system compressed.  Block
compressed data clearly needs to be uncompressed.

In a lot of situations this makes block compression undesirable.  We don't want to loose an
important current performance optimization to add block compression if we can avoid it.

> SequenceFile should compress blocks, not individual entries
> -----------------------------------------------------------
>
>                 Key: HADOOP-54
>                 URL: http://issues.apache.org/jira/browse/HADOOP-54
>             Project: Hadoop
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 0.2.0
>            Reporter: Doug Cutting
>         Assigned To: Arun C Murthy
>             Fix For: 0.5.0
>
>         Attachments: VIntCompressionResults.txt
>
>
> SequenceFile will optionally compress individual values.  But both compression and performance
would be much better if sequences of keys and values are compressed together.  Sync marks
should only be placed between blocks.  This will require some changes to MapFile too, so that
all file positions stored there are the positions of blocks, not entries within blocks.  Probably
this can be accomplished by adding a getBlockStartPosition() method to SequenceFile.Writer.

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