ParquetRecordBatchStream API to fetch the next row group while decoding
#6559
Comments
masonh22
added
the
enhancement
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This is a very interesting idea -- I think it is a good one as this is quite a common case. |
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Right now users can implement their own pre-fetching logic (e.g. to batch object store requests) but they don't know what ranges of data will be used. Maybe the API could be something that calculated the required ranges based on RowGroupMetadata that were selected what file ranges would be needed To start this this project, I would recommend that we create a motivating example (with some sort of mocked out S3 thing) showing how we wanted to read the data |
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I was thinking that the pre-fetch logic could be pushed into the ParquetRecordBatchStream itself. I made a proof-of-concept of this here: masonh22@4f682b1 I didn't add any performance tests, but I confirmed that this sped things up in my own project by effectively removing the cost of decoding since reading the data takes longer than decoding it. |
Is your feature request related to a problem or challenge? Please describe what you are trying to do.
I've noticed low CPU utilization when reading from filesystems with low
bandwidth using a
ParquetRecordBatchStream. This appears to be caused by thefact that the stream fetches row group data on demand rather than ahead of
time. In my specific scenario, I'm reading a parquet file from s3 with four
128MB row groups. It takes ~2 seconds to fetch the data and ~500ms to decode the
entire row group. In all, it takes around 10 seconds to read and decode the
entire file.
Describe the solution you'd like
I'd like to add the option for
ParquetRecordBatchStreamto fetch the data forthe next row group while decoding data for the current row group.
Describe alternatives you've considered
Additional context
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