[ https://issues.apache.org/jira/browse/HBASE-4218?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13159391#comment-13159391 ]
Phabricator commented on HBASE-4218: ------------------------------------ tedyu has commented on the revision "[jira] [HBASE-4218] Delta encoding for keys in HFile". Nice work, Mikhail and Jacek. Please add category to the new tests. Are there performance numbers for various encoders other than Prefix encoder ? INLINE COMMENTS src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV1.java:337 As Matt pointed out, the return value should be stored in hfileBlock so that we don't incur double encoding. src/main/java/org/apache/hadoop/hbase/io/hfile/HFileReaderV2.java:305 Similar to the case in HFileReaderV1, return value should be stored in dataBlock. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderAlgorithms.java:33 Matt suggested alternative names for DeltaEncoding: KeyValueEncoding, DataBlockEncoding, HCellEncoding, BlockEncoding. DataBlockEncoding sounds good. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:405 Misspelling: comperator should be comparator. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderAlgorithms.java:65 Javadoc doesn't match actual class name. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/FastDiffDeltaEncoder.java:53 The tail should read '128 bit encoding' src/main/java/org/apache/hadoop/hbase/io/deltaencoder/FastDiffDeltaEncoder.java:28 This class is only used locally. It should be an inner class. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:49 Tail should read '128 bit encoding' src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:346 Please remove extra blank line. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DiffKeyDeltaEncoder.java:28 Please change this class to inner class. src/main/java/org/apache/hadoop/hbase/io/deltaencoder/DeltaEncoderBufferTooSmallException.java:22 Should read 'which indicates' 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 -- 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