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From "Jacek Migdal (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-4218) Delta Encoding of KeyValues (aka prefix compression)
Date Sat, 08 Oct 2011 00:59:29 GMT

    [ https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13123337#comment-13123337
] 

Jacek Migdal commented on HBASE-4218:
-------------------------------------

Performance results on production data.

 CopyKeyDeltaEncoder:
   Compression performance:   1136.33 MB/s (+/- 60.91 MB/s)
   Decompression performance: 373.29 MB/s (+/- 281.22 MB/s)
 BitsetKeyDeltaEncoder:
   Compression performance:   147.57 MB/s (+/- 0.58 MB/s)
   Decompression performance: 166.78 MB/s (+/- 54.81 MB/s)
 PrefixKeyDeltaEncoder:
   Compression performance:   293.94 MB/s (+/- 1.97 MB/s)
   Decompression performance: 233.61 MB/s (+/- 91.97 MB/s)
 FastDiffDeltaEncoder:
   Compression performance:   203.47 MB/s (+/- 0.37 MB/s)
   Decompression performance: 196.77 MB/s (+/- 43.22 MB/s)
 DiffKeyDeltaEncoder:
   Compression performance:   187.74 MB/s (+/- 0.24 MB/s)
   Decompression performance: 163.13 MB/s (+/- 12.17 MB/s)
 LZO:
   Compression performance:   260.35 MB/s (+/- 0.76 MB/s)
   Decompression performance: 173.45 MB/s (+/- 76.13 MB/s)
 CopyKeyDeltaEncoder
   Saved bytes:                  -4
   Key compression ratio:        -0.00 %
   All compression ratio:        -0.00 %
   LZO compressed size:      152019
   LZO compression ratio:        85.79 %
 BitsetKeyDeltaEncoder
   Saved bytes:              747061
   Key compression ratio:        75.46 %
   All compression ratio:        69.82 %
   LZO compressed size:      124438
   LZO compression ratio:        88.37 %
 PrefixKeyDeltaEncoder
   Saved bytes:              831602
   Key compression ratio:        84.00 %
   All compression ratio:        77.72 %
   LZO compressed size:      117285
   LZO compression ratio:        89.04 %
 FastDiffDeltaEncoder
   Saved bytes:              935275
   Key compression ratio:        94.47 %
   All compression ratio:        87.41 %
   LZO compressed size:       94360
   LZO compression ratio:        91.18 %
 DiffKeyDeltaEncoder
   Saved bytes:              909175
   Key compression ratio:        91.84 %
   All compression ratio:        84.97 %
   LZO compressed size:       96597
   LZO compression ratio:        90.97 %
 Total KV prefix length:      80000
 Total key length:           910000
 Total key redundancy:       781606
 Total value length:          80000

DeltaEncodingSeekPerformance


 BlockDeltaEncoder onDisk='NONE' inCache='NONE' inMemory=false
   Read speed:          63.99 (MB/s)
   Seeks per second: 54901.21 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='BITSET' inMemory=false
   Read speed:          46.73 (MB/s)
   Seeks per second: 13570.50 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='PREFIX' inMemory=false
   Read speed:          55.88 (MB/s)
   Seeks per second: 20298.89 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='DIFF' inMemory=false
   Read speed:          54.39 (MB/s)
   Seeks per second: 15082.79 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='FAST_DIFF' inMemory=false
   Read speed:          54.12 (MB/s)
   Seeks per second: 15432.61 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='NONE' inMemory=true
   Read speed:          64.37 (MB/s)
   Seeks per second: 56779.82 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='BITSET' inMemory=true
   Read speed:          35.42 (MB/s)
   Seeks per second: 46170.87 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='PREFIX' inMemory=true
   Read speed:          43.54 (MB/s)
   Seeks per second: 60108.48 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='DIFF' inMemory=true
   Read speed:          40.62 (MB/s)
   Seeks per second: 48779.68 (#/s)
 BlockDeltaEncoder onDisk='NONE' inCache='FAST_DIFF' inMemory=true
   Read speed:          40.76 (MB/s)
   Seeks per second: 57291.22 (#/s)

                
> 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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