[ https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Yang He updated HBASE-4218: --------------------------- Summary: Data Block Encoding of KeyValues (aka delta encoding / prefix compression (was: Data Block Encoding of KeyValues (aka delta encoding / prefix compression)) > 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, 4218-2012-01-14.txt, 4218-v16.txt, 4218.txt, > ASF.LICENSE.NOT.GRANTED--D1659.1.patch, > ASF.LICENSE.NOT.GRANTED--D1659.2.patch, > ASF.LICENSE.NOT.GRANTED--D1659.3.patch, > ASF.LICENSE.NOT.GRANTED--D447.1.patch, > ASF.LICENSE.NOT.GRANTED--D447.10.patch, > ASF.LICENSE.NOT.GRANTED--D447.11.patch, > ASF.LICENSE.NOT.GRANTED--D447.12.patch, > ASF.LICENSE.NOT.GRANTED--D447.13.patch, > ASF.LICENSE.NOT.GRANTED--D447.14.patch, > ASF.LICENSE.NOT.GRANTED--D447.15.patch, > ASF.LICENSE.NOT.GRANTED--D447.16.patch, > ASF.LICENSE.NOT.GRANTED--D447.17.patch, > ASF.LICENSE.NOT.GRANTED--D447.18.patch, > ASF.LICENSE.NOT.GRANTED--D447.19.patch, > ASF.LICENSE.NOT.GRANTED--D447.2.patch, > ASF.LICENSE.NOT.GRANTED--D447.20.patch, > ASF.LICENSE.NOT.GRANTED--D447.21.patch, > ASF.LICENSE.NOT.GRANTED--D447.22.patch, > ASF.LICENSE.NOT.GRANTED--D447.23.patch, > ASF.LICENSE.NOT.GRANTED--D447.24.patch, > ASF.LICENSE.NOT.GRANTED--D447.25.patch, > ASF.LICENSE.NOT.GRANTED--D447.26.patch, > ASF.LICENSE.NOT.GRANTED--D447.3.patch, ASF.LICENSE.NOT.GRANTED--D447.4.patch, > ASF.LICENSE.NOT.GRANTED--D447.5.patch, ASF.LICENSE.NOT.GRANTED--D447.6.patch, > ASF.LICENSE.NOT.GRANTED--D447.7.patch, ASF.LICENSE.NOT.GRANTED--D447.8.patch, > ASF.LICENSE.NOT.GRANTED--D447.9.patch, Data-block-encoding-2011-12-23.patch, > Delta-encoding-2012-01-17_11_09_09.patch, > Delta-encoding-2012-01-25_00_45_29.patch, > Delta-encoding-2012-01-25_16_32_14.patch, > Delta-encoding.patch-2011-12-22_11_52_07.patch, > Delta-encoding.patch-2012-01-05_15_16_43.patch, > Delta-encoding.patch-2012-01-05_16_31_44.patch, > Delta-encoding.patch-2012-01-05_16_31_44_copy.patch, > Delta-encoding.patch-2012-01-05_18_50_47.patch, > Delta-encoding.patch-2012-01-07_14_12_48.patch, > Delta-encoding.patch-2012-01-13_12_20_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 -- This message was sent by Atlassian JIRA (v6.1.4#6159)