[jira] [Commented] (HBASE-4218) Delta Encoding of KeyValues (aka prefix compression)

["Phabricator (Commented) (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13167721#comment-13167721 ] 

Phabricator commented on HBASE-4218:
------------------------------------

mbautin has commented on the revision "[jira] [HBASE-4218] Delta encoding for keys in HFile".

  See responses inline. I will follow up with a new version of the diff shortly.

INLINE COMMENTS
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderAlgorithms.java:65 Removed javadoc comments from these enum items, because they don't add information.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderAlgorithms.java:33 Jacek's delta encoding algorithm names are {Bitset,Prefix,Diff,FastDiff}KeyDeltaEncoder. I don't see how Matt's alternative encoding names correspond to these. I will follow up with Matt on the JIRA.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderBufferTooSmallException.java:22 Fixed, thanks!
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:28 Done.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:49 Done.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:346 Done.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:405 Done.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/FastDiffDeltaEncoder.java:28 Done.
  src/main/java/org/apache/hadoop/hbase/io/deltaencoder/FastDiffDeltaEncoder.java:53 Done.
  src/main/java/org/apache/hadoop/hbase/io/hfile/EmptyBlockDeltaEncoder.java:29 Done.
  src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV1.java:337 Fixed. As far as I understand, this fix takes advantage of the fact that delta encoding API is designed to be idempotent (i.e. when we do beforeBlockCache and give the already-encoded block to afterReadFromDiskAndPuttingIntoCache, it will work correctly).

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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