[GitHub] [orc] wgtmac commented on issue #1475: [C++] Order of row index streams does not match the order of streams in the file footer

["wgtmac (via GitHub)" <gi...@apache.org>]

wgtmac commented on issue #1475:
URL: https://github.com/apache/orc/issues/1475#issuecomment-1519092569

   Thanks for reporting the issue! @vuule
   
   The order of data streams are **NOT FIXED** meaning that:
   - In a direct-encoded string columns, `DATA stream` can be placed **BEFORE** or **AFTER** `LENGTH stream`. Same flexibility for `PRESENT stream`.
   - Even data streams of different columns can be interleaved.
   
   However, the order of positions in a index stream is **FIXED**. So for a direct-encoded string column, its `INDEX stream` always put positions in this order: `PRESENT stream` (if exists), `DATA stream` and `LENGTH stream`.
   
   I checked the [specs](https://orc.apache.org/specification/ORCv1/) and it does not state this clearly. It would be a good time to document this as well. @deshanxiao 
   
   


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