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Parquet v3 read concurrency
zvonand
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releasy
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Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):
Parquet reader now fetches compressed chunks from storage far ahead of decoding. Compressed data is small, so many reads stay in flight while decoding catches up at its own pace — cold scans are no longer bottlenecked on storage latency (S3).
Read-ahead and decoding get separate memory and thread budgets, tunable via
input_format_parquet_prefetch_memory_fraction(0.6) andinput_format_parquet_decode_thread_fraction(0.375) (#2235 by @UnamedRus).Cherry-picked from #2235.
Number of changes to bring parquet v3 reader perf closer to arrow based