Add public API for decoding parquet footer #1804
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tustvold
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alamb
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Jun 7, 2022
parquet/src/arrow/async_reader.rs
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| self.seek(SeekFrom::End(-8 - metadata_len)).await?; | ||
| let metadata_len = decode_footer(&buf)?; | ||
| self.seek(SeekFrom::End(-8 - metadata_len as i64)).await?; |
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I wonder if we can make this magic 8 a const somewhere to help readablility -- or maybe it is already FOOTER_SIZE
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It actually makes the code harder to read, as FOOTER_SIZE is usize but then SeekFrom wants i64... The compiler checks the array size, and I don't suppose it is likely to change, so I think we should be fine.
Edit: Introduced FOOTER_SIZE_I64 to workaround
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Which issue does this PR close?
Part of #1605
Part of #1163
Rationale for this change
This makes it possible for AsyncChunkReader implementations to implement
AsyncChunkReader::get_metadatawithout having to duplicate functionality from the parquet crate. It also feeds into the story of separating the IO to fetch bytes, from the logic to decode those bytes.What changes are included in this PR?
Tweaks the methods used to read parquet to allow them to be exposed publicly
Are there any user-facing changes?
The sync reader will no longer pre-fetch bytes when reading the footer. I'm inclined to think this will be complete wash in terms of performance, and makes the implementation simpler.