[
https://issues.apache.org/jira/browse/PARQUET-2108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17457490#comment-17457490
]
Balaji K commented on PARQUET-2108:
-----------------------------------
I now see this extra text under Dictionary encoding:
"Data page format: the bit width used to encode the entry ids stored as 1 byte
(max bit width = 32). Followed by the values encoded using RLE/Bit packed"
However, putting in the length as described the Hybrid RLE algorithm won't make
the Data page correct or be readable I think. The implementation is saying bit
width + data.
Would appreciate some clarity on this subject and I can help update the docs :)
> Specification for RLEDictionary encoding is incorrect.
> ------------------------------------------------------
>
> Key: PARQUET-2108
> URL: https://issues.apache.org/jira/browse/PARQUET-2108
> Project: Parquet
> Issue Type: Bug
> Reporter: Balaji K
> Priority: Major
>
> The [spec for RLE
> Dictionary|[https://github.com/apache/parquet-format/blob/master/Encodings.md#dictionary-encoding-plain_dictionary--2-and-rle_dictionary--8]]
> encoding says the "length of the encoded-data" is placed before the
> "encoded-data". Reproducing the first 3 lines here:
> ```
> rle-bit-packed-hybrid: <length> <encoded-data>
> length := length of the <encoded-data> in bytes stored as 4 bytes little
> endian (unsigned int32)
> encoded-data := <run>*
> ```
> However, this is not true. Parquet-MR implementation does not encode the
> length in front of the data. It encodes bitWidth as 1 byte. See
> [implementation|[https://github.com/apache/parquet-mr/blob/01a5d074829ad4cf4de1f662d54fe7bceb4bef63/parquet-column/src/main/java/org/apache/parquet/column/values/dictionary/DictionaryValuesWriter.java#L173]].
> I'm proposing the spec be updated to state the above clearly.
> see discussion here:
> [https://lists.apache.org/thread/p45tpjd5r03qbswtpr7xfy072josnjxs]
>
--
This message was sent by Atlassian Jira
(v8.20.1#820001)
