apply_cache_image returned a copy of the whole file with the image's
entries written in, and File (mmap by default), MmapFile and LazyFile
used that copy for every read: opening a 1 GiB sparse file with an image
needed 2 GB of memory, and an 8 GiB one aborted the process, where
de2a53f (which ignored the image) opened them in a few MB.
The metadata parsers read one contiguous slice, so the image still has
to be laid over the file's bytes; it is now laid over a private copy
that costs only the pages it touches:
- clawhdf5_format::superblock_ext::CacheImage decodes the image into an
entry list (address, offset in the block, length) and applies it to
any destination; cache_image_state tells an opener whether the file
has no image, a loadable one, or one libhdf5 cannot load;
apply_cache_image_in_place is for readers that own their buffer.
apply_cache_image and metadata_view (which copied) are gone.
- clawhdf5_io::HDF5Read::private_copy returns a writable private copy
of a reader's bytes: MmapReader gives a MAP_PRIVATE copy-on-write
mapping (memmap2 map_copy), so only the pages the entries land on are
copied; the default copies the bytes (in-memory readers).
- File, MmapFile and LazyFile write the image into that mapping
(crate::cache_image). File::from_bytes / open_buffered patch their own
buffer in place, copying only the image block, as libhdf5 does. A
file without an image is read straight from the mapping, unchanged.
An image entry that runs past the end of file is now refused: libhdf5
checks only that it starts inside the file, and the images libhdf5
writes never do this, but those bytes have nowhere to go in a view of
the file.
Tests: tests/cache_image_memory.rs has libhdf5 (through ctypes) add an
image to a 1 GiB sparse file and bounds resident-memory growth for all
three openers at 256 MiB; it fails on the previous commit (File::open
grew 2,148,720,640 bytes). reader.rs zero_copy_tests check that a file
without an image is read from the mapping itself and that an image goes
into a copy-on-write mapping, not a heap copy; clawhdf5-io checks that
private_copy writes never reach the reader or the file.
Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Four independent write-path improvements:
1. Cache compressed chunks between Pass 1 and Pass 2 (chunked_write.rs,
file_writer.rs): the two-pass layout writer previously called
build_chunked_data_at_ext() twice per chunked dataset — once in Pass 1
to get blob sizes and once in Pass 2 with real addresses. Add
PrecompressedChunks / precompress_chunks() / build_chunked_data_from_
precompressed() to compress once in Pass 1, cache the result, and only
rebuild the address-dependent index structures in Pass 2. Expected
~2× speedup for chunked+deflate writes (512×512 deflate: 3.33ms → ~1.7ms).
2. SIMD-vectorisable shuffle filter (filters.rs): replace the naïve O(N·S)
nested loop with an unrolled u32-load path for 4-byte elements (f32) and
a cache-blocked tile loop for all other sizes. LLVM auto-vectorises the
4-byte path into SSE2/AVX2/NEON byte-deinterleave sequences.
3. Zstd benchmark variant (h5bench_write.rs): add write_2d_chunked_zstd
group measuring Zstd level 3 vs deflate level 6 side-by-side. Also fix
the existing write_2d_chunked benchmark — the clawhdf5 path was missing
.with_deflate(6), making the comparison apples-to-oranges. Add arXiv-
backed doc recommendation on DatasetBuilder::with_zstd().
4. Zero-copy HNSW save (hnsw.rs, clawhdf5-io/lib.rs): add
FileWriter::write_bytes_owned(Vec<u8>) that takes ownership to avoid the
full-file clone in write_all_bytes(&[u8]). HNSW::save_to_hdf5 uses it.
Co-Authored-By: Claude Sonnet 4.6 <[email protected]>
