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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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