Struct OverflowRegion 

pub struct OverflowRegion { /* private fields */ }

mmap-backed overflow region owned by a single core.

Uses a bump allocator within the mmap’d file with a free-list for slot reuse. When a slot is freed, it’s added to the free-list so future writes of equal or smaller size can reclaim the space without advancing the bump cursor.

Not Send or Sync — it’s single-thread owned.

Implementations

impl OverflowRegion

pub const DEFAULT_INITIAL_CAPACITY: usize

Default initial mmap size.

Corresponds to MemoryTuning::overflow_initial_bytes.

pub const DEFAULT_MAX_CAPACITY: usize

Default maximum capacity (prevents unbounded growth).

Corresponds to MemoryTuning::overflow_max_bytes.

pub fn open(path: &Path) -> Result<Self>

Open or create an overflow region at the given path.

If the file doesn’t exist, it’s created with the initial capacity. If the file exists, it’s mapped at current size.

pub fn open_with_config( path: &Path, initial_capacity: usize, max_capacity: usize, ) -> Result<Self>

Open or create an overflow region with explicit initial and maximum capacity.

Use this when applying runtime config from MemoryTuning.

pub fn open_with_capacity(path: &Path, initial_capacity: usize) -> Result<Self>

Open or create an overflow region with a specific initial capacity.

pub fn madvise_state(&self) -> Option<c_int>

The madvise hint currently in effect on the mapped region.

pub fn write(&mut self, data: &[u8], engine: EngineId) -> Result<usize>

Write data to the overflow region and return the slot index.

First attempts to reuse a freed slot from the free-list (best-fit). Falls back to bump allocation if no suitable free slot exists.

pub fn read(&self, slot_index: usize) -> Result<&[u8]>

Read data from a slot (returns a slice into the mmap).

pub fn free(&mut self, slot_index: usize) -> Result<()>

Mark a slot as freed and add it to the free-list for reuse.

pub fn used_bytes(&self) -> usize

Current utilization of the mmap region in bytes.

pub fn capacity(&self) -> usize

Total capacity of the mmap region in bytes.

pub fn path(&self) -> &Path

Path to the backing overflow file.

pub fn slot_count(&self) -> usize

Number of slots (occupied or freed).

Trait Implementations

impl Drop for OverflowRegion

fn drop(&mut self)

Executes the destructor for this type.