Coalesce contiguous ranges in LocalFileSystem::get_ranges#777
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Merge only contiguous/overlapping ranges (gap 0) into a single read, so we never read unrequested bytes but still collapse many adjacent ranges into far fewer syscalls. A fast path skips the coalescing bookkeeping entirely when nothing merges, avoiding overhead for disjoint ranges. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Closes: #778
LocalFileSystem::get_rangesissued one read per range. This coalesces contiguous/overlapping ranges into a single read, collapsing many adjacent ranges into far fewer syscalls.On a warm-cache benchmark, many adjacent small ranges drop ~2.6× (e.g. 1024 × 4 KiB contiguous: ~700 µs → ~260 µs); disjoint ranges are unchanged.
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