Struct PlainMmapBacking 

pub struct PlainMmapBacking { /* private fields */ }

Zero-copy VectorSegmentBacking backed by a plaintext NDVS mmap segment.

Vectors and surrogate IDs are served as slices directly into the mmap region — no allocation on the read path.

Send + Sync rationale

MmapVectorSegment is declared !Send + !Sync because it holds a *const u8 field (base) pointing into the mmap region. Raw pointers are conservative: the compiler cannot know whether the pointee is safe to share.

The mmap region behind base is:

• mapped with PROT_READ | MAP_PRIVATE — never mutated through this pointer after construction,
• valid for exactly the lifetime of the MmapVectorSegment (the descriptor _fd keeps the file open; munmap runs in Drop),
• not thread-affine — the OS virtual-memory subsystem treats it as a process-global read-only region.

All access to base goes through get_vector / get_surrogate / prefetch, which derive shared borrows (&[f32], &[u8]) that live no longer than &self. No &mut path exists. Multiple threads reading distinct vectors concurrently is safe for the same reason &[T] is Sync.

The Arc<MmapVectorSegment> wrapper ensures the segment (and therefore the mmap region) outlives any &[f32] slice handed out through this type.

SAFETY: given the above invariants, treating PlainMmapBacking as Send + Sync is correct.

Implementations

impl PlainMmapBacking

pub fn new(seg: MmapVectorSegment) -> Self

Wrap a MmapVectorSegment that is not yet reference-counted.

MmapVectorSegment holds a *const u8 raw pointer which makes it !Send + !Sync by default. The unsafe impl Send + Sync on PlainMmapBacking (see struct-level doc comment) establishes the safety invariants; clippy cannot see through the Arc to the impl, so we suppress the lint here.

pub fn from_arc(seg: Arc<MmapVectorSegment>) -> Self

Wrap an already reference-counted segment.

Useful when the same segment is shared with other consumers (e.g. a crate::collection::VectorCollection that also owns the segment for direct SIMD scan).

pub fn segment(&self) -> &Arc<MmapVectorSegment>

Access the underlying segment.

Trait Implementations

impl Send for PlainMmapBacking

impl Sync for PlainMmapBacking

impl VectorSegmentBacking for PlainMmapBacking

fn len(&self) -> usize

Number of vectors stored in this segment.

fn dim(&self) -> usize

Dimensionality of each stored vector.

fn get_vector(&self, id: u32) -> Option<&[f32]>

Fetch one vector by local position id (0..len).

fn get_surrogate(&self, id: u32) -> Option<u64>

Surrogate id for a local position.

fn prefetch(&self, id: u32)

Optional prefetch hint.

fn is_empty(&self) -> bool

Returns true when the segment contains no vectors.