jorgecarleitao commented on a change in pull request #170: URL: https://github.com/apache/parquet-format/pull/170#discussion_r606750973
########## File path: rle-bitpacked.md ########## @@ -0,0 +1,120 @@ +# RLE-Bitpacked hybrid encoder + +The RLE-Bitpacked hybrid encoder is a parquet-specific encoder that combines +two well known encoding strategies, [RLE](https://en.wikipedia.org/wiki/Run-length_encoding) +and bitpacking. Note that "combine" here means this encoder allows both encodings +within the same stream, and, during encoding, it can switch between them. + +This encoder is only used to encode integer values that may either represent definition levels, +representation levels or ids of dictionary-encoded pages. Note that this encoder +supports integers that can be represented in less than 8 bits. + +This document uses [LSB](https://en.wikipedia.org/wiki/Bit_numbering#Least_significant_bit) +to identify bits. In this representation, a byte is represented +by `[b7 b6 b5 b4 b3 b2 b1 b0]` where `b0` is the first bit. + +This document uses MUST, SHOULD, etc. according to [RFC-8174](https://tools.ietf.org/html/rfc8174). + +## Decoding + +Decoding a stream of bytes (denoted as `[a1, a2, a3, ...]`) assumes a specific `bit_width` +indicating the number of bits necessary to represent the largest encoded integer in the stream. + +The `bit_width` MUST be sufficient to represent the largest encoded integer on the +stream or the result is undefined. + +The first 4 bytes of the stream MUST represent a little-endian unsigned integer (`uint32`) +denoting the length of the rest of the stream. For example, `[4u8, 0, 0, 0]` announces Review comment: yep. I wanted to add the type information to make sure that people understand that this was an array of bytes, not `uint32` or something, but I have no preference into exactly we state that it is a byte / `u8`. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: [email protected]
