Struct Lsm 

pub struct Lsm<const K: usize, const V: usize> { /* private fields */ }

Implementations

impl<const K: usize, const V: usize> Lsm<K, V>

pub fn recover<P: AsRef<Path>>(p: P) -> Result<Lsm<K, V>>

Recover the LSM off disk. Make sure to never recover a DB using different K, V parameters than it was created with, or there may be data loss.

This is an O(N) operation and involves reading all previously written sstables and the log, to recover all data into an in-memory BTreeMap.

pub fn recover_with_config<P: AsRef<Path>>( p: P, config: Config, ) -> Result<Lsm<K, V>>

Recover the LSM, and provide custom options around IO and merging. All values in the Config object are safe to change across restarts, unlike the fixed K and V lengths for data in the database.

pub fn insert(&mut self, k: [u8; K], v: [u8; V]) -> Result<Option<[u8; V]>>

Writes a KV pair into the Lsm, returning the previous value if it existed. This operation might involve blocking for a very brief moment as a 32kb BufWriter wrapping the log file is flushed.

If you require blocking until all written data is durable, use the Lsm::flush method below.

pub fn remove(&mut self, k: &[u8; K]) -> Result<Option<[u8; V]>>

Removes a KV pair from the Lsm, returning the previous value if it existed. This operation might involve blocking for a very brief moment as a 32kb BufWriter wrapping the log file is flushed.

If you require blocking until all written data is durable, use the Lsm::flush method below.

pub fn write_batch( &mut self, write_batch: &[([u8; K], Option<[u8; V]>)], ) -> Result<()>

Apply a set of updates to the Lsm and log them to disk in a way that will be recovered only if every update is present.

pub fn flush(&mut self) -> Result<()>

Blocks until all log data has been written out to disk and fsynced. If the log file has grown above a certain threshold, it will be compacted into a new sstable and the log file will be truncated after the sstable has been written, fsynced, and the sstable directory has been fsyced.

pub fn stats(&mut self) -> Result<Stats>

Methods from Deref<Target = BTreeMap<[u8; K], [u8; V]>>

pub fn get<Q>(&self, key: &Q) -> Option<&V>

where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns a reference to the value corresponding to the key.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);

pub fn get_key_value<Q>(&self, k: &Q) -> Option<(&K, &V)>

where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns the key-value pair corresponding to the supplied key. This is potentially useful:

• for key types where non-identical keys can be considered equal;
• for getting the &K stored key value from a borrowed &Q lookup key; or
• for getting a reference to a key with the same lifetime as the collection.

The supplied key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples

use std::cmp::Ordering;
use std::collections::BTreeMap;

#[derive(Clone, Copy, Debug)]
struct S {
    id: u32,
    name: &'static str, // ignored by equality and ordering operations
}

impl PartialEq for S {
    fn eq(&self, other: &S) -> bool {
        self.id == other.id
    }
}

impl Eq for S {}

impl PartialOrd for S {
    fn partial_cmp(&self, other: &S) -> Option<Ordering> {
        self.id.partial_cmp(&other.id)
    }
}

impl Ord for S {
    fn cmp(&self, other: &S) -> Ordering {
        self.id.cmp(&other.id)
    }
}

let j_a = S { id: 1, name: "Jessica" };
let j_b = S { id: 1, name: "Jess" };
let p = S { id: 2, name: "Paul" };
assert_eq!(j_a, j_b);

let mut map = BTreeMap::new();
map.insert(j_a, "Paris");
assert_eq!(map.get_key_value(&j_a), Some((&j_a, &"Paris")));
assert_eq!(map.get_key_value(&j_b), Some((&j_a, &"Paris"))); // the notable case
assert_eq!(map.get_key_value(&p), None);

pub fn first_key_value(&self) -> Option<(&K, &V)>

where K: Ord,

Returns the first key-value pair in the map. The key in this pair is the minimum key in the map.

Examples

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
assert_eq!(map.first_key_value(), None);
map.insert(1, "b");
map.insert(2, "a");
assert_eq!(map.first_key_value(), Some((&1, &"b")));

pub fn last_key_value(&self) -> Option<(&K, &V)>

where K: Ord,

Returns the last key-value pair in the map. The key in this pair is the maximum key in the map.

Examples

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "b");
map.insert(2, "a");
assert_eq!(map.last_key_value(), Some((&2, &"a")));

pub fn contains_key<Q>(&self, key: &Q) -> bool

where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

Returns true if the map contains a value for the specified key.

The key may be any borrowed form of the map’s key type, but the ordering on the borrowed form must match the ordering on the key type.

Examples

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);

pub fn range<T, R>(&self, range: R) -> Range<'_, K, V>

where T: Ord + ?Sized, K: Borrow<T> + Ord, R: RangeBounds<T>,

Constructs a double-ended iterator over a sub-range of elements in the map. The simplest way is to use the range syntax min..max, thus range(min..max) will yield elements from min (inclusive) to max (exclusive). The range may also be entered as (Bound<T>, Bound<T>), so for example range((Excluded(4), Included(10))) will yield a left-exclusive, right-inclusive range from 4 to 10.

Panics

Panics if range start > end. Panics if range start == end and both bounds are Excluded.

Examples

use std::collections::BTreeMap;
use std::ops::Bound::Included;

let mut map = BTreeMap::new();
map.insert(3, "a");
map.insert(5, "b");
map.insert(8, "c");
for (&key, &value) in map.range((Included(&4), Included(&8))) {
    println!("{key}: {value}");
}
assert_eq!(Some((&5, &"b")), map.range(4..).next());

pub fn iter(&self) -> Iter<'_, K, V>

Gets an iterator over the entries of the map, sorted by key.

Examples

use std::collections::BTreeMap;

let mut map = BTreeMap::new();
map.insert(3, "c");
map.insert(2, "b");
map.insert(1, "a");

for (key, value) in map.iter() {
    println!("{key}: {value}");
}

let (first_key, first_value) = map.iter().next().unwrap();
assert_eq!((*first_key, *first_value), (1, "a"));

pub fn keys(&self) -> Keys<'_, K, V>

Gets an iterator over the keys of the map, in sorted order.

Examples

use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(2, "b");
a.insert(1, "a");

let keys: Vec<_> = a.keys().cloned().collect();
assert_eq!(keys, [1, 2]);

pub fn values(&self) -> Values<'_, K, V>

Gets an iterator over the values of the map, in order by key.

Examples

use std::collections::BTreeMap;

let mut a = BTreeMap::new();
a.insert(1, "hello");
a.insert(2, "goodbye");

let values: Vec<&str> = a.values().cloned().collect();
assert_eq!(values, ["hello", "goodbye"]);

pub fn len(&self) -> usize

Returns the number of elements in the map.

Examples

use std::collections::BTreeMap;

let mut a = BTreeMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Examples

use std::collections::BTreeMap;

let mut a = BTreeMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());

pub fn lower_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>

where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

🔬This is a nightly-only experimental API. (btree_cursors)

Returns a Cursor pointing at the gap before the smallest key greater than the given bound.

Passing Bound::Included(x) will return a cursor pointing to the gap before the smallest key greater than or equal to x.

Passing Bound::Excluded(x) will return a cursor pointing to the gap before the smallest key greater than x.

Passing Bound::Unbounded will return a cursor pointing to the gap before the smallest key in the map.

Examples

#![feature(btree_cursors)]

use std::collections::BTreeMap;
use std::ops::Bound;

let map = BTreeMap::from([
    (1, "a"),
    (2, "b"),
    (3, "c"),
    (4, "d"),
]);

let cursor = map.lower_bound(Bound::Included(&2));
assert_eq!(cursor.peek_prev(), Some((&1, &"a")));
assert_eq!(cursor.peek_next(), Some((&2, &"b")));

let cursor = map.lower_bound(Bound::Excluded(&2));
assert_eq!(cursor.peek_prev(), Some((&2, &"b")));
assert_eq!(cursor.peek_next(), Some((&3, &"c")));

let cursor = map.lower_bound(Bound::Unbounded);
assert_eq!(cursor.peek_prev(), None);
assert_eq!(cursor.peek_next(), Some((&1, &"a")));

pub fn upper_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>

where K: Borrow<Q> + Ord, Q: Ord + ?Sized,

🔬This is a nightly-only experimental API. (btree_cursors)

Returns a Cursor pointing at the gap after the greatest key smaller than the given bound.

Passing Bound::Included(x) will return a cursor pointing to the gap after the greatest key smaller than or equal to x.

Passing Bound::Excluded(x) will return a cursor pointing to the gap after the greatest key smaller than x.

Passing Bound::Unbounded will return a cursor pointing to the gap after the greatest key in the map.

Examples

#![feature(btree_cursors)]

use std::collections::BTreeMap;
use std::ops::Bound;

let map = BTreeMap::from([
    (1, "a"),
    (2, "b"),
    (3, "c"),
    (4, "d"),
]);

let cursor = map.upper_bound(Bound::Included(&3));
assert_eq!(cursor.peek_prev(), Some((&3, &"c")));
assert_eq!(cursor.peek_next(), Some((&4, &"d")));

let cursor = map.upper_bound(Bound::Excluded(&3));
assert_eq!(cursor.peek_prev(), Some((&2, &"b")));
assert_eq!(cursor.peek_next(), Some((&3, &"c")));

let cursor = map.upper_bound(Bound::Unbounded);
assert_eq!(cursor.peek_prev(), Some((&4, &"d")));
assert_eq!(cursor.peek_next(), None);

Trait Implementations

impl<const K: usize, const V: usize> Deref for Lsm<K, V>

type Target = BTreeMap<[u8; K], [u8; V]>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<const K: usize, const V: usize> Drop for Lsm<K, V>

fn drop(&mut self)

Executes the destructor for this type.