Document when the ParquetRecordBatchReader will re-read metadata #5887
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alamb
commented
Jun 14, 2024
| /// construct multiple separate readers, for example, to distribute readers | ||
| /// across multiple threads | ||
| /// | ||
| /// 2. Using a cached copy of the [`ParquetMetadata`] rather than reading it |
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I also added the second and important usecase of not re-reading the metadata on subsequent reads
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Cheaply clonaable is good :-) |
tustvold
approved these changes
Jun 14, 2024
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Thank you for the reviews |
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Which issue does this PR close?
N/A
Rationale for this change
While working on apache/datafusion#10701 and discussing with @marsupialtail I finally figured out how to use the page index with cached parquet metadata without extra object store requests.
However, I think it is quite tricky and subtle, so it would be good to document this in the parquet crate itself so I don't have to go spelunking in the future.
What changes are included in this PR?
Document when
ArrowReaderMetadata::loadwill make object store calls when using the page indexAre there any user-facing changes?
Just docs