parquet::ArrowWriter show allow writing Bloom filters before the end of the file #5859
Labels
enhancement
Any new improvement worthy of a entry in the changelog
parquet
Changes to the parquet crate
Is your feature request related to a problem or challenge? Please describe what you are trying to do.
https://parquet.apache.org/docs/file-format/bloomfilter/#file-format mentions two ways to layout Bloom Filters: either write each Bloom Filter after its row group, or write all Bloom Filters at the end; then write pointers to Bloom Filters in the footer.
The
parquet
crate opts for writing all Bloom Filters at the end, while computing them while each row group is being written. This means Bloom Filters need to be kept in memory while files are being written, which can take significant space. In my use case, ~4TB of Bloom filters while writing a 20TB table.Describe the solution you'd like
Either switch to the other layout (interleaved with row groups), provide an option to switch between the two, or allow users to flush when they want to.
Describe alternatives you've considered
Expecting users to close the ArrowWriter from time to time, and opening a new one. This would mitigate the memory usage, but not entirely remove it. When writing in parallel from multiple threads, it also means they need to stagger re-openings when writing many files in parallel in order to avoid spikes in RAM.
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