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perf: try pread like zarrs's use of File::read_exact_at #4039

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perf: try pread like zarrs's use of File::read_exact_at #4039

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perf: try `pread` like `zarrs`'s use of `File::read_exact_at`
ilan-gold Jun 5, 2026
7e1eafd
Merge branch 'main' into ig/pread
ilan-gold Jun 5, 2026
72cb294
perf:move size
ilan-gold Jun 5, 2026
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48 changes: 36 additions & 12 deletions src/zarr/storage/_local.py
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Original file line number Diff line number Diff line change
Expand Up @@ -30,18 +30,42 @@
def _get(path: Path, prototype: BufferPrototype, byte_range: ByteRequest | None) -> Buffer:
if byte_range is None:
return prototype.buffer.from_bytes(path.read_bytes())
with path.open("rb") as f:
size = f.seek(0, io.SEEK_END)
if isinstance(byte_range, RangeByteRequest):
f.seek(byte_range.start)
return prototype.buffer.from_bytes(f.read(byte_range.end - f.tell()))
elif isinstance(byte_range, OffsetByteRequest):
f.seek(byte_range.offset)
elif isinstance(byte_range, SuffixByteRequest):
f.seek(max(0, size - byte_range.suffix))
else:
raise TypeError(f"Unexpected byte_range, got {byte_range}.")
return prototype.buffer.from_bytes(f.read())

if hasattr(os, "pread"):
# Use pread on systems that support it (Unix-like)
fd = os.open(path, os.O_RDONLY)
try:
if isinstance(byte_range, RangeByteRequest):
length = byte_range.end - byte_range.start
data = os.pread(fd, length, byte_range.start)
elif isinstance(byte_range, OffsetByteRequest):
file_size = os.fstat(fd).st_size
length = max(0, file_size - byte_range.offset)
data = os.pread(fd, length, byte_range.offset)
elif isinstance(byte_range, SuffixByteRequest):
file_size = os.fstat(fd).st_size
offset = max(0, file_size - byte_range.suffix)
length = file_size - offset
data = os.pread(fd, length, offset)
else:
raise TypeError(f"Unexpected byte_range, got {byte_range}.")
return prototype.buffer.from_bytes(data)
finally:
os.close(fd)
else:
# Fallback to seek/read for systems without pread (e.g., Windows)
with path.open("rb") as f:
if isinstance(byte_range, RangeByteRequest):
f.seek(byte_range.start)
return prototype.buffer.from_bytes(f.read(byte_range.end - f.tell()))
elif isinstance(byte_range, OffsetByteRequest):
f.seek(byte_range.offset)
elif isinstance(byte_range, SuffixByteRequest):
size = f.seek(0, io.SEEK_END)
f.seek(max(0, size - byte_range.suffix))
else:
raise TypeError(f"Unexpected byte_range, got {byte_range}.")
return prototype.buffer.from_bytes(f.read())


if sys.platform == "win32":
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