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https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13123597#comment-13123597
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Ted Yu commented on HBASE-4218:
-------------------------------

EmptyBlockDeltaEncoder, CompressionState, BlockDeltaEncoder need license.
                
> Delta Encoding of KeyValues  (aka prefix compression)
> -----------------------------------------------------
>
>                 Key: HBASE-4218
>                 URL: https://issues.apache.org/jira/browse/HBASE-4218
>             Project: HBase
>          Issue Type: Improvement
>          Components: io
>    Affects Versions: 0.94.0
>            Reporter: Jacek Migdal
>              Labels: compression
>         Attachments: open-source.diff
>
>
> A compression for keys. Keys are sorted in HFile and they are usually very 
> similar. Because of that, it is possible to design better compression than 
> general purpose algorithms,
> It is an additional step designed to be used in memory. It aims to save 
> memory in cache as well as speeding seeks within HFileBlocks. It should 
> improve performance a lot, if key lengths are larger than value lengths. For 
> example, it makes a lot of sense to use it when value is a counter.
> Initial tests on real data (key length = ~ 90 bytes , value length = 8 bytes) 
> shows that I could achieve decent level of compression:
>  key compression ratio: 92%
>  total compression ratio: 85%
>  LZO on the same data: 85%
>  LZO after delta encoding: 91%
> While having much better performance (20-80% faster decompression ratio than 
> LZO). Moreover, it should allow far more efficient seeking which should 
> improve performance a bit.
> It seems that a simple compression algorithms are good enough. Most of the 
> savings are due to prefix compression, int128 encoding, timestamp diffs and 
> bitfields to avoid duplication. That way, comparisons of compressed data can 
> be much faster than a byte comparator (thanks to prefix compression and 
> bitfields).
> In order to implement it in HBase two important changes in design will be 
> needed:
> -solidify interface to HFileBlock / HFileReader Scanner to provide seeking 
> and iterating; access to uncompressed buffer in HFileBlock will have bad 
> performance
> -extend comparators to support comparison assuming that N first bytes are 
> equal (or some fields are equal)
> Link to a discussion about something similar:
> http://search-hadoop.com/m/5aqGXJEnaD1/hbase+windows&subj=Re+prefix+compression

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