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From "Arun C Murthy (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-54) SequenceFile should compress blocks, not individual entries
Date Tue, 18 Jul 2006 04:02:15 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-54?page=comments#action_12421776 ] 
            
Arun C Murthy commented on HADOOP-54:
-------------------------------------

Couple of implementation thoughts/refinements (thanks  by Eric) I wanted to bring to everyone's
attention:

  a) We could use BytesWritables for keys/values (which maintain their own sizes), thus the
header would then only be:
      sync,no.of k/v pairs, compressed-keys-size, compressed-values-size, compressedKeysBlob,
compressedValuesBlob, sync

  b) Use the 'zero-compressed-int-length' that Milind is exporting from recordio for the 'integer'
values in the header to save some bytes.

Thoughts? Other refinements?

thanks,
Arun

> 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: Michel Tourn
>             Fix For: 0.5.0
>
>
> 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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