[GitHub] [arrow] zeroshade commented on pull request #13277: ARROW-16638: [Go][Parquet] Fix skipping large number of rows in boolean columns

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zeroshade commented on PR #13277:
URL: https://github.com/apache/arrow/pull/13277#issuecomment-1147662934

   @mdepero In the `parquet/internal/utils` package there is a function `BytesToBools` which explicitly is an efficient conversion from bitpacked bytes to a `[]bool`. It assumes that the slices are already sized appropriately (`len(out)` should equal `len(in)*8`).
   
   That being said, there might be a way we can get around this by changing the implementation slightly. 
   
   Since the `columnChunkReader` is embedded in the typed readers, we don't "technically" need to do `cr.columnChunkReader.skipValues(...` and could instead do `cr.skipValues(...`. I only specified the `cr.columnChunkReader` portion to make it explicit. The benefit there if we convert it to being just `cr.skipValues` is that we can then override the `skipValues` function for the `BooleanColumnChunkReader` to allocate the *correct* amount of scratch space, it does result in some duplication of code but I think it's a better solution to avoid the extra allocation where possible. As another, forward looking idea, I'd probably want to have the scratch space use a pool of buffers rather than allocating a new scratch space for every skip but that can be done as a later change. Anyways, did that all make sense as something you could do? 
   
   Let me know if you have any questions. Thanks again for this!


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