[ http://issues.apache.org/jira/browse/HADOOP-54?page=all ]
Arun C Murthy updated HADOOP-54:
--------------------------------
Attachment: VIntCompressionResults.txt
Here's a test run analysing compression of VInts (exported from recordio).
Essentially we get almost 50% savings (either with zlib/gzip) of
compressed-VInts v/s uncompressed raw integers on disk (4bytes per int) ...
Sounds like a good reason to go ahead with Eric's proposal to compress not only
keys/values but also keyLengthsBlock/valueLengthsBlock? I'll go ahead with this
for now unless anyone objects...
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: 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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