[GitHub] [arrow-rs] tustvold opened a new issue, #4155: Splice Parquet Data

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

tustvold opened a new issue, #4155:
URL: https://github.com/apache/arrow-rs/issues/4155

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   A common request is to be able to combine parquet files together without re-encoding data (#557) (#4150). However, correctly translating the metadata is non-trivial, and requires care to ensure the relevant file offsets are correctly updated.
   
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   I would like an API on `SerializedRowGroupWriter` that lets me append an existing ColumnChunk from another source. For example,
   
   ```
   /// Splice a column from another file without decoding it
   ///
   /// This can be used for efficiently concatenating or projecting parquet data
   pub fn splice_column<R: ChunkReader>(&mut self, reader: &R, metadata: &ColumnChunkMetaData) -> Result<()> {
   ```
   
   I originally debated making the signature
   
   ```
   pub fn splice_column(&mut self, column: &dyn PageReader) -> Result<()> {
   ```
   
   But this runs into a couple of problems
   
   * The PageReader returns uncompressed, decoded pages (although the value data is still encoded)
   * It isn't clear how to preserve the page index or any bloom filter information
   
   I also debated allowing appending pages individually, however, in addition to the above problems it runs into:
   
   * A column chunk can only have a single dictionary page
   * The compression codec is specified at the column chunk level
   
   The downside of the `ChunkReader` API is that potentially someone could pass a reader that doesn't match the `ColumnChunkMetaData`, which would result in an inconsistent parquet file. I'm inclined to think this isn't a problem, as there are plenty of other ways to generate an invalid "parquet" file :sweat_smile: 
   
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[GitHub] [arrow-rs] tustvold commented on issue #4155: Splice Parquet Data

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

tustvold commented on issue #4155:
URL: https://github.com/apache/arrow-rs/issues/4155#issuecomment-1573883277

   `label_issue.py` automatically added labels {'parquet'} from #4265


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[GitHub] [arrow-rs] tustvold closed issue #4155: Splice Parquet Data

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

tustvold closed issue #4155: Splice Parquet Data
URL: https://github.com/apache/arrow-rs/issues/4155


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