Overhaul Parquet dictionary handling #14194
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… reader to read dictionary entries, turn dictionary in a vector, and just emit dictionary vectors on top of that as results
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Not sure if this is feature or main just yet |
hannes
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Oct 22, 2024
Fix an issue when reading from partial pages with the new dictionary handling added in #14194
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This PR changes the way we handle dictionary-encoded data from Parquet files. Previously, we would use a type-specific handling of dictionaries, e.g. an array of string_t for strings or just a blob for integers.
With this PR, we change this to a generic solution where the dictionary is read using the "plain" reading infrastructure into a DuckDB Vector. Later, we turn the offsets into this dictionary into a selection vector and Slice the dictionary vector. This has the nice effect that Parquet dictionary references are turned into DuckDB dictionary vectors. In addition, we add generic bounds checks for dictionary offsets to ensure no crashes can occur from corrupt Parquet files.
This PR also adds a benchmark that shows that handling dictionaries is actually slightly faster with this PR, especially for large dictionaries.