Struct Cache

pub struct Cache<DK, DV> { /* private fields */ }

A cache, mapping [u8] keys to [u8] values.

This cache wraps generic byte storage that implements AsRef<[u8]>. This is most commonly a memory-mapped file, Mmap.

For serializing a stream of (key, value) pairs, see Builder.

Implementations

impl<DK, DV> Cache<DK, DV>

where DK: AsRef<[u8]>, DV: AsRef<[u8]>,

pub fn new(index_bytes: DK, value_bytes: DV) -> Result<Self, Error>

pub fn index(&self) -> &Map<DK>

Access the internal fst::Map used for mapping keys to value offsets.

pub fn value_bytes(&self) -> &[u8]

The entire byte slice storing all values.

pub fn get_value_offset(&self, key: &[u8]) -> Option<u64>

Returns the byte offset of the value for key, if it exists.

The returned offset can be used with the value_at_offset method.

pub unsafe fn offset_transmuted_value<T>(&self, offset: usize) -> &T

Transmutes the bytes starting at offset into a T reference.

Safety

offset must point to a valid representation of T in the value_bytes region of memory.

pub unsafe fn get_transmuted_value<T>(&self, key: &[u8]) -> Option<&T>

Transmutes the bytes pointed to by key (if any) into a T reference.

Safety

key must point to a valid representation of T in the value_bytes region of memory.

pub fn range<K, R>(&self, key_range: R) -> StreamBuilder<'_>

where K: AsRef<[u8]>, R: RangeBounds<K>,

Returns a streaming iterator over (key, value offset) pairs.

The offset is a byte offset pointing to the start of the value for that key.

pub fn first<const N: usize>(&self) -> Option<([u8; N], u64)>

Returns the (lexicographical) first (key, value) pair.

Panics

If the actual first key is longer than N.

pub fn last<const N: usize>(&self) -> Option<([u8; N], u64)>

Returns the (lexicographical) last (key, value) pair.

Panics

If the actual last key is longer than N.

pub fn last_le<const N: usize>( &self, upper_bound: &[u8], ) -> Option<([u8; N], u64)>

Finds the (lexicographical) greatest key k such that k <= upper_bound.

Panics

If the found key is longer than N.

impl Cache<Mmap, Mmap>

pub unsafe fn map_paths( index_path: impl AsRef<Path>, value_path: impl AsRef<Path>, ) -> Result<Self, Error>

Maps the files at index_path and value_path to read-only virtual memory ranges.

Safety

See Mmap.

pub unsafe fn map_files( index_file: &File, value_file: &File, ) -> Result<Self, Error>

Mapsindex_file and value_file to read-only virtual memory ranges.

Safety

See Mmap.