[ https://issues.apache.org/jira/browse/IMPALA-6658?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Thomas Tauber-Marshall reassigned IMPALA-6658: ---------------------------------------------- Assignee: Andrew Sherman > Parquet RLE encoding can waste space with small repeated runs > ------------------------------------------------------------- > > Key: IMPALA-6658 > URL: https://issues.apache.org/jira/browse/IMPALA-6658 > Project: IMPALA > Issue Type: Improvement > Components: Backend > Reporter: Csaba Ringhofer > Assignee: Andrew Sherman > Priority: Minor > Labels: parquet, ramp-up > > Currently RleEncoder creates repeated runs from 8 repeated values, which can > be less space efficient than bit-packed if bit width is 1 or 2. In the worst > case, the whole data page can be ~2X larger if bit width is 1, and ~1.25X > larger if bit is 2 compared to bit-packing. > A comment in rle_encoding.h writes different numbers, but it probably does > not calculate with the overhead of splitting long runs into smaller ones > (every run adds +1 byte for its length): > https://github.com/apache/impala/blob/8079cd9d2a87051f81a41910b74fab15e35f36ea/be/src/util/rle-encoding.h#L62 > Note that if the data page is compressed, this size difference probably > disappears, but the larger uncompressed buffer size can still affect > performance. > Parquet RLE encoding is described here: https://github.com/apache/parquet- > format/blob/master/Encodings.md#run-length-encoding--bit-packing-hybrid-rle--3 -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-all-unsubscr...@impala.apache.org For additional commands, e-mail: issues-all-h...@impala.apache.org