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Hadoop QA commented on HBASE-4218: ---------------------------------- -1 overall. Here are the results of testing the latest attachment http://issues.apache.org/jira/secure/attachment/12509029/4218-v16.txt against trunk revision . +1 @author. The patch does not contain any @author tags. +1 tests included. The patch appears to include 104 new or modified tests. -1 javadoc. The javadoc tool appears to have generated -138 warning messages. +1 javac. The applied patch does not increase the total number of javac compiler warnings. -1 findbugs. The patch appears to introduce 82 new Findbugs (version 1.3.9) warnings. +1 release audit. The applied patch does not increase the total number of release audit warnings. -1 core tests. The patch failed these unit tests: org.apache.hadoop.hbase.io.hfile.TestHFileBlock org.apache.hadoop.hbase.mapreduce.TestImportTsv org.apache.hadoop.hbase.mapred.TestTableMapReduce org.apache.hadoop.hbase.mapreduce.TestHFileOutputFormat Test results: https://builds.apache.org/job/PreCommit-HBASE-Build/650//testReport/ Findbugs warnings: https://builds.apache.org/job/PreCommit-HBASE-Build/650//artifact/trunk/patchprocess/newPatchFindbugsWarnings.html Console output: https://builds.apache.org/job/PreCommit-HBASE-Build/650//console This message is automatically generated. > 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-v16.txt, D447.1.patch, D447.10.patch, > D447.11.patch, D447.12.patch, D447.13.patch, D447.14.patch, D447.15.patch, > D447.16.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 -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators: https://issues.apache.org/jira/secure/ContactAdministrators!default.jspa For more information on JIRA, see: http://www.atlassian.com/software/jira