kevinjqliu opened a new pull request, #3971:
URL: https://github.com/apache/iceberg-python/pull/3971

   # Rationale for this change
   
   Raise the PyArrow FileIO buffer default from 1 MiB to 8 MiB. Use the same 
default for input/output streams and the Parquet scan and positional-delete 
readers. Regular Parquet scans already specified 8 MiB.
   
   8 MiB is a reasonable starting point for sequential object-store reads. 
[Hadoop’s S3 
prefetcher](https://hadoop.apache.org/docs/current/hadoop-aws/tools/hadoop-aws/prefetching.html)
 and [Trino’s Parquet 
reader](https://github.com/trinodb/trino/blob/ea6ca09ae29eea442e01a79bbc650987e8897ec1/lib/trino-parquet/src/main/java/io/trino/parquet/ParquetReaderOptions.java#L25-L29)
 use that size for read blocks. These are precedents, not evidence of a 
measured speedup here.
   
   ## Are these changes tested?
   
   Added assertions for the constructor default and both FileIO factories, with 
and without a buffer-size override. Focused PyArrow and Avro tests pass.
   
   ## Are there any user-facing changes?
   
   The default stream buffer increases to 8 MiB for reads and writes, including 
output files converted to input files. Existing `buffer-size` overrides still 
work. Seekable reads and Arrow’s S3 multipart upload size are unchanged.


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