[ https://issues.apache.org/jira/browse/HIVE-3874?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13548750#comment-13548750 ]
Owen O'Malley commented on HIVE-3874: ------------------------------------- Namit, Yes, it has dictionary encoding for strings. The dictionary enables both better compression and makes push down filters much more efficient. The dictionaries are local to only the row group, so that row groups can be processed independently of each other. Currently, strings are always dictionary encoded, but it would make sense to allow the writer to pick whether the column should be encoded directly or using a dictionary. > Create a new Optimized Row Columnar file format for Hive > -------------------------------------------------------- > > Key: HIVE-3874 > URL: https://issues.apache.org/jira/browse/HIVE-3874 > Project: Hive > Issue Type: Improvement > Components: Serializers/Deserializers > Reporter: Owen O'Malley > Assignee: Owen O'Malley > > There are several limitations of the current RC File format that I'd like to > address by creating a new format: > * each column value is stored as a binary blob, which means: > ** the entire column value must be read, decompressed, and deserialized > ** the file format can't use smarter type-specific compression > ** push down filters can't be evaluated > * the start of each row group needs to be found by scanning > * user metadata can only be added to the file when the file is created > * the file doesn't store the number of rows per a file or row group > * there is no mechanism for seeking to a particular row number, which is > required for external indexes. > * there is no mechanism for storing light weight indexes within the file to > enable push-down filters to skip entire row groups. > * the type of the rows aren't stored in the file -- This message is automatically generated by JIRA. If you think it was sent incorrectly, please contact your JIRA administrators For more information on JIRA, see: http://www.atlassian.com/software/jira