Struct sled::Tree

pub struct Tree { /* fields omitted */ }

A flash-sympathetic persistent lock-free B+ tree

Examples

let t = sled::Db::start_default("path_to_my_database").unwrap();

t.set(b"yo!", b"v1".to_vec());
assert!(t.get(b"yo!").unwrap().unwrap() == &*b"v1".to_vec());

t.cas(
    b"yo!",                // key
    Some(b"v1"),           // old value, None for not present
    Some(b"v2".to_vec()),  // new value, None for delete
).unwrap();

let mut iter = t.scan(b"a non-present key before yo!");
// assert_eq!(iter.next(), Some(Ok((b"yo!".to_vec(), b"v2".to_vec()))));
// assert_eq!(iter.next(), None);

t.del(b"yo!");
assert_eq!(t.get(b"yo!"), Ok(None));

Methods

impl Tree

Important traits for Subscriber

impl Iterator for Subscriber type Item = Event;

pub fn watch_prefix(&self, prefix: Vec<u8>) -> Subscriber

Subscribe to Events that happen to keys that have the specified prefix. Events for particular keys are guaranteed to be witnessed in the same order by all threads, but threads may witness different interleavings of Events across different keys. If subscribers don't keep up with new writes, they will cause new writes to block. There is a buffer of 1024 items per Subscriber. This can be used to build reactive and replicated systems.

Examples

use sled::{Event, ConfigBuilder};
let config = ConfigBuilder::new().temporary(true).build();

let tree = sled::Db::start(config).unwrap();

// watch all events by subscribing to the empty prefix
let mut events = tree.watch_prefix(vec![]);

let tree_2 = tree.clone();
let thread = std::thread::spawn(move || {
    tree.set(vec![0], vec![1]).unwrap();
});

// events is a blocking `Iterator` over `Event`s
for event in events.take(1) {
    match event {
        Event::Set(key, value) => assert_eq!(key, vec![0]),
        Event::Merge(key, partial_value) => {}
        Event::Del(key) => {}
    }
}

thread.join().unwrap();

pub fn clear(&self) -> Result<()>

Clears the Tree, removing all values.

Note that this is not atomic.

pub fn name(&self) -> Vec<u8>

Returns the name of the tree.

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

Flushes all dirty IO buffers and calls fsync. If this succeeds, it is guaranteed that all previous writes will be recovered if the system crashes. Returns the number of bytes flushed during this call.

pub fn contains_key<K: AsRef<[u8]>>(&self, key: K) -> Result<bool>

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

pub fn get<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<IVec>>

Retrieve a value from the Tree if it exists.

pub fn get_lt<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<(Vec<u8>, IVec)>>

Retrieve the key and value before the provided key, if one exists.

Examples

use sled::{ConfigBuilder, Error};
let config = ConfigBuilder::new().temporary(true).build();

let tree = sled::Db::start(config).unwrap();

for i in 0..10 {
    tree.set(vec![i], vec![i]).expect("should write successfully");
}

assert!(tree.get_lt(vec![]).unwrap().is_none());
assert!(tree.get_lt(vec![0]).unwrap().is_none());
assert!(tree.get_lt(vec![1]).unwrap().unwrap().1 == vec![0]);
assert!(tree.get_lt(vec![9]).unwrap().unwrap().1 == vec![8]);
assert!(tree.get_lt(vec![10]).unwrap().unwrap().1 == vec![9]);
assert!(tree.get_lt(vec![255]).unwrap().unwrap().1 == vec![9]);

pub fn get_gt<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<(Vec<u8>, IVec)>>

Retrieve the next key and value from the Tree after the provided key.

Examples

use sled::{ConfigBuilder, Error};
let config = ConfigBuilder::new().temporary(true).build();

let tree = sled::Db::start(config).unwrap();

for i in 0..10 {
    tree.set(vec![i], vec![i]).expect("should write successfully");
}

assert!(tree.get_gt(vec![]).unwrap().unwrap().1 == vec![0]);
assert!(tree.get_gt(vec![0]).unwrap().unwrap().1 == vec![1]);
assert!(tree.get_gt(vec![1]).unwrap().unwrap().1 == vec![2]);
assert!(tree.get_gt(vec![8]).unwrap().unwrap().1 == vec![9]);
assert!(tree.get_gt(vec![9]).unwrap().is_none());

pub fn cas<K: AsRef<[u8]>>(
    &self,
    key: K,
    old: Option<&[u8]>,
    new: Option<Vec<u8>>
) -> Result<Result<(), Option<IVec>>>

Compare and swap. Capable of unique creation, conditional modification, or deletion. If old is None, this will only set the value if it doesn't exist yet. If new is None, will delete the value if old is correct. If both old and new are Some, will modify the value if old is correct. If Tree is read-only, will do nothing.

Examples

use sled::{ConfigBuilder, Error};
let config = ConfigBuilder::new().temporary(true).build();
let t = sled::Db::start(config).unwrap();

// unique creation
assert_eq!(t.cas(&[1], None, Some(vec![1])), Ok(Ok(())));

// conditional modification
assert_eq!(t.cas(&[1], Some(&*vec![1]), Some(vec![2])), Ok(Ok(())));

// conditional deletion
assert_eq!(t.cas(&[1], Some(&[2]), None), Ok(Ok(())));
assert_eq!(t.get(&[1]), Ok(None));

pub fn set<K: AsRef<[u8]>>(
    &self,
    key: K,
    value: Vec<u8>
) -> Result<Option<IVec>>

Set a key to a new value, returning the old value if it was set.

pub fn del<K: AsRef<[u8]>>(&self, key: K) -> Result<Option<IVec>>

Delete a value, returning the last result if it existed.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Db::start(config).unwrap();
t.set(&[1], vec![1]);
assert_eq!(t.del(&*vec![1]).unwrap().unwrap(), vec![1]);
assert_eq!(t.del(&*vec![1]), Ok(None));

pub fn merge<K: AsRef<[u8]>>(&self, key: K, value: Vec<u8>) -> Result<()>

Merge state directly into a given key's value using the configured merge operator. This allows state to be written into a value directly, without any read-modify-write steps. Merge operators can be used to implement arbitrary data structures.

Panics

Calling merge will panic if no merge operator has been configured.

Examples

fn concatenate_merge(
  _key: &[u8],               // the key being merged
  old_value: Option<&[u8]>,  // the previous value, if one existed
  merged_bytes: &[u8]        // the new bytes being merged in
) -> Option<Vec<u8>> {       // set the new value, return None to delete
  let mut ret = old_value
    .map(|ov| ov.to_vec())
    .unwrap_or_else(|| vec![]);

  ret.extend_from_slice(merged_bytes);

  Some(ret)
}

let config = sled::ConfigBuilder::new()
  .temporary(true)
  .merge_operator(concatenate_merge)
  .build();

let tree = sled::Db::start(config).unwrap();

let k = b"k1";

tree.set(k, vec![0]);
tree.merge(k, vec![1]);
tree.merge(k, vec![2]);
// assert_eq!(tree.get(k).unwrap().unwrap(), vec![0, 1, 2]);

// sets replace previously merged data,
// bypassing the merge function.
tree.set(k, vec![3]);
// assert_eq!(tree.get(k), Ok(Some(vec![3])));

// merges on non-present values will add them
tree.del(k);
tree.merge(k, vec![4]);
// assert_eq!(tree.get(k).unwrap().unwrap(), vec![4]);

Important traits for Iter<'a>

impl<'a> Iterator for Iter<'a> type Item = Result<(Vec<u8>, IVec)>;

pub fn iter(&self) -> Iter

Create a double-ended iterator over the tuples of keys and values in this tree.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Db::start(config).unwrap();
t.set(&[1], vec![10]);
t.set(&[2], vec![20]);
t.set(&[3], vec![30]);
let mut iter = t.iter();
// assert_eq!(iter.next(), Some(Ok((vec![1], vec![10]))));
// assert_eq!(iter.next(), Some(Ok((vec![2], vec![20]))));
// assert_eq!(iter.next(), Some(Ok((vec![3], vec![30]))));
// assert_eq!(iter.next(), None);

Important traits for Iter<'a>

impl<'a> Iterator for Iter<'a> type Item = Result<(Vec<u8>, IVec)>;

pub fn scan<K>(&self, key: K) -> Iter where
    K: AsRef<[u8]>, 

Create a double-ended iterator over tuples of keys and values, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new()
    .temporary(true)
    .build();
let t = sled::Db::start(config).unwrap();

t.set(b"0", vec![0]).unwrap();
t.set(b"1", vec![10]).unwrap();
t.set(b"2", vec![20]).unwrap();
t.set(b"3", vec![30]).unwrap();
t.set(b"4", vec![40]).unwrap();
t.set(b"5", vec![50]).unwrap();

let mut r = t.scan(b"2");
assert_eq!(r.next().unwrap().unwrap().0, b"2");
assert_eq!(r.next().unwrap().unwrap().0, b"3");
assert_eq!(r.next().unwrap().unwrap().0, b"4");
assert_eq!(r.next().unwrap().unwrap().0, b"5");
assert_eq!(r.next(), None);
let mut r = t.scan(b"2").rev();
assert_eq!(r.next().unwrap().unwrap().0, b"2");
assert_eq!(r.next().unwrap().unwrap().0, b"1");
assert_eq!(r.next().unwrap().unwrap().0, b"0");
assert_eq!(r.next(), None);

Important traits for Iter<'a>

impl<'a> Iterator for Iter<'a> type Item = Result<(Vec<u8>, IVec)>;

pub fn range<K, R>(&self, range: R) -> Iter where
    K: AsRef<[u8]>,
    R: RangeBounds<K>, 

Create a double-ended iterator over tuples of keys and values, where the keys fall within the specified range.

Examples

let config = sled::ConfigBuilder::new()
    .temporary(true)
    .build();
let t = sled::Db::start(config).unwrap();

t.set(b"0", vec![0]).unwrap();
t.set(b"1", vec![10]).unwrap();
t.set(b"2", vec![20]).unwrap();
t.set(b"3", vec![30]).unwrap();
t.set(b"4", vec![40]).unwrap();
t.set(b"5", vec![50]).unwrap();

let start: &[u8] = b"2";
let end: &[u8] = b"4";
let mut r = t.range(start..end);
assert_eq!(r.next().unwrap().unwrap().0, b"2");
assert_eq!(r.next().unwrap().unwrap().0, b"3");
assert_eq!(r.next(), None);

let start = b"2".to_vec();
let end = b"4".to_vec();
let mut r = t.range(start..end).rev();
assert_eq!(r.next().unwrap().unwrap().0, b"3");
assert_eq!(r.next().unwrap().unwrap().0, b"2");
assert_eq!(r.next(), None);

pub fn keys<'a, K>(
    &'a self,
    key: K
) -> impl 'a + DoubleEndedIterator<Item = Result<Vec<u8>>> where
    K: AsRef<[u8]>, 

Create a double-ended iterator over keys, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Db::start(config).unwrap();
t.set(&[1], vec![10]);
t.set(&[2], vec![20]);
t.set(&[3], vec![30]);
let mut iter = t.scan(&*vec![2]);
// assert_eq!(iter.next(), Some(Ok(vec![2])));
// assert_eq!(iter.next(), Some(Ok(vec![3])));
// assert_eq!(iter.next(), None);

pub fn values<'a, K>(
    &'a self,
    key: K
) -> impl 'a + DoubleEndedIterator<Item = Result<IVec>> where
    K: AsRef<[u8]>, 

Create a double-ended iterator over values, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Db::start(config).unwrap();
t.set(&[1], vec![10]);
t.set(&[2], vec![20]);
t.set(&[3], vec![30]);
let mut iter = t.scan(&*vec![2]);
// assert_eq!(iter.next(), Some(Ok(vec![20])));
// assert_eq!(iter.next(), Some(Ok(vec![30])));
// assert_eq!(iter.next(), None);

pub fn len(&self) -> usize

Returns the number of elements in this tree.

Beware: performs a full O(n) scan under the hood.

pub fn is_empty(&self) -> bool

Returns true if the Tree contains no elements.

Trait Implementations

impl Clone for Tree

fn clone(&self) -> Tree

Returns a copy of the value.

default fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Send for Tree

impl Sync for Tree

impl<'a> IntoIterator for &'a Tree

type Item = Result<(Vec<u8>, IVec)>

The type of the elements being iterated over.

type IntoIter = Iter<'a>

Which kind of iterator are we turning this into?

Important traits for Iter<'a>

impl<'a> Iterator for Iter<'a> type Item = Result<(Vec<u8>, IVec)>;

fn into_iter(self) -> Iter<'a>

Creates an iterator from a value.

impl Debug for Tree

fn fmt(&self, f: &mut Formatter) -> Result<(), Error>

Formats the value using the given formatter.