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https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159531#comment-13159531
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Phabricator commented on HBASE-4218:
------------------------------------
todd has commented on the revision "[jira] [HBASE-4218] Delta encoding for keys
in HFile".
I only got through a little bit of the giant patch, but it looks well done
and decently unit-tested, so I'm +1 once you have some cluster testing results
that show it basically works :)
Test-plan should include an upgrade test from an unpatched HFile v2 format
and an HFile v1 (0.90) upgrade
INLINE COMMENTS
src/main/java/org/apache/hadoop/hbase/HColumnDescriptor.java:99 seems odd
that the type of this is boolean whereas the IN_CACHE one is an Algorithm type.
If it's a requirement that the algo be the same, then maybe rename this one to
be DEFAULT_DELTA_ENCODING_IN_MEMORY_ENABLED
src/main/java/org/apache/hadoop/hbase/KeyValue.java:2022 This interface name
isn't quite clear to me, since it doesn't compare prefixes. Maybe
SuffixComparator? Or ComparatorAssumingEqualPrefix (though that's a bit
lengthy)?
src/main/java/org/apache/hadoop/hbase/io/deltaencoder/BitsetKeyDeltaEncoder.java:34-42
should use inline HTML to format this right
src/main/java/org/apache/hadoop/hbase/io/deltaencoder/BitsetKeyDeltaEncoder.java:56
s/writeHere/out/g for consistent style
src/main/java/org/apache/hadoop/hbase/io/deltaencoder/BitsetKeyDeltaEncoder.java:69
s/source/in/g
src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoder.java:32-35
use HTML <ul>...
src/main/java/org/apache/hadoop/hbase/io/hfile/AbstractHFileWriter.java:90
typo
src/main/java/org/apache/hadoop/hbase/io/hfile/EmptyBlockDeltaEncoder.java:29
maybe "NoOpDeltaEncoder" is a better name? (it's not that the block is empty)
REVISION DETAIL
https://reviews.facebook.net/D447
> 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
> Assignee: Mikhail Bautin
> Labels: compression
> Attachments: D447.1.patch, D447.2.patch, D447.3.patch, D447.4.patch,
> D447.5.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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