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https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13176709#comment-13176709
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Phabricator commented on HBASE-4218:
------------------------------------
mcorgan has commented on the revision "[jira] [HBASE-4218] HFile data block
encoding (delta encoding)".
I'm porting the TRIE encoding algorithm over to this new patch, so am able to
review a little better in eclipse than on review board. Couple things I've
noticed so far:
INLINE COMMENTS
src/main/java/org/apache/hadoop/hbase/io/encoding/DataBlockEncodings.java:32
The enum nested in a class is unusual. Would a more typical approach be to
call it DataBlockEncoding (singular) and make that the enum, eliminating the
nested "Algorithm"?
So you would have DataBlockEncoding.BITSET, etc.
This would help elsewhere in the codebase since it will eliminate the
confusion with the unfortunately named compression "Algorithm" (GZIP, LZO)
src/main/java/org/apache/hadoop/hbase/io/encoding/BufferedDataBlockEncoder.java:121
This method was added before getKeyValueObject(), so I see why it happened
this way, but this method should probably be called getKeyValueBuffer() or
getKeyValueByteBuffer(), and the below method should be called getKeyValue()
src/main/java/org/apache/hadoop/hbase/io/encoding/BufferedDataBlockEncoder.java:134
rename to getKeyValue()
REVISION DETAIL
https://reviews.facebook.net/D447
> Data Block Encoding of KeyValues (aka delta encoding / 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
> Assignee: Mikhail Bautin
> Labels: compression
> Fix For: 0.94.0
>
> Attachments: 0001-Delta-encoding-fixed-encoded-scanners.patch,
> 0001-Delta-encoding.patch, D447.1.patch, D447.10.patch, D447.11.patch,
> D447.12.patch, D447.13.patch, D447.2.patch, D447.3.patch, D447.4.patch,
> D447.5.patch, D447.6.patch, D447.7.patch, D447.8.patch, D447.9.patch,
> Data-block-encoding-2011-12-23.patch,
> Delta-encoding.patch-2011-12-22_11_52_07.patch,
> Delta_encoding_with_memstore_TS.patch, 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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