Add IPC FileDecoder #5249
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Add IPC FileDecoder #5249
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tustvold
commented
Dec 27, 2023
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| /// let trailer_start = buffer.len() - 10; | ||
| /// let footer_len = read_footer_length(buffer[trailer_start..].try_into().unwrap()).unwrap(); | ||
| /// let footer = root_as_footer(&buffer[trailer_start - footer_len..trailer_start]).unwrap(); | ||
| /// | ||
| /// let back = fb_to_schema(footer.schema().unwrap()); | ||
| /// assert_eq!(&back, schema.as_ref()); | ||
| /// | ||
| /// let mut decoder = FileDecoder::new(schema, footer.version()); | ||
| /// | ||
| /// // Read dictionaries | ||
| /// for block in footer.dictionaries().iter().flatten() { | ||
| /// let block_len = block.bodyLength() as usize + block.metaDataLength() as usize; | ||
| /// let data = buffer.slice_with_length(block.offset() as _, block_len); | ||
| /// decoder.read_dictionary(&block, &data).unwrap(); | ||
| /// } | ||
| /// | ||
| /// // Read record batch | ||
| /// let batches = footer.recordBatches().unwrap(); | ||
| /// assert_eq!(batches.len(), 1); // Only wrote a single batch | ||
| /// | ||
| /// let block = batches.get(0); | ||
| /// let block_len = block.bodyLength() as usize + block.metaDataLength() as usize; | ||
| /// let data = buffer.slice_with_length(block.offset() as _, block_len); | ||
| /// let back = decoder.read_record_batch(block, &data).unwrap().unwrap(); |
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This is still somewhat verbose, but I couldn't see an easy way to reduce this further that didn't end up in knots with self-referential structs (as flatbuffers borrow data)
tustvold
commented
Dec 27, 2023
| pub fn read_record_batch( | ||
| &self, | ||
| block: &Block, | ||
| buf: &Buffer, |
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It is perhaps worth noting that this interface won't allow pushing down column projection to IO, I think this is a bridge we cross when we add support for this.
This was referenced Dec 28, 2023
7 tasks
viirya
reviewed
Dec 29, 2023
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| /// Read the dictionary with the given block and data buffer | ||
| pub fn read_dictionary(&mut self, block: &Block, buf: &Buffer) -> Result<(), ArrowError> { | ||
| let message = self.read_message(buf)?; |
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Not bit deal but seems we didn't check for metadata version for DictionaryBatch before. Maybe it was missed before.
viirya
approved these changes
Dec 30, 2023
viirya
reviewed
Dec 30, 2023
Co-authored-by: Liang-Chi Hsieh <[email protected]>
😆 -- love it! |
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Which issue does this PR close?
Closes #5153
Closes #5165
Closes #5252
Part of #1207
Rationale for this change
In a similar vein to arrow-csv and arrow-json this extracts a low-level, push-based interface for decoding files. This lends itself to use-cases that need more control over how IO is performed, for example:
What changes are included in this PR?
Are there any user-facing changes?