[][src]Struct sled::Tree

pub struct Tree { /* fields omitted */ }

A flash-sympathetic persistent lock-free B+ tree

Examples

let t = sled::Tree::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
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Load existing or create a new Tree with a default configuration.

Load existing or create a new Tree.

Important traits for 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::Tree::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();

Generate a monotonic ID. Not guaranteed to be contiguous. Written to disk every idgen_persist_interval operations, followed by a blocking flush. During recovery, we take the last recovered generated ID and add 2x the idgen_persist_interval to it. While persisting, if the previous persisted counter wasn't synced to disk yet, we will do a blocking flush to fsync the latest counter, ensuring that we will never give out the same counter twice.

Clears the Tree, removing all values.

Note that this is not atomic.

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

Retrieve a value from the Tree if it exists.

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::Tree::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]);

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::Tree::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());

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::Tree::start(config).unwrap();

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

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

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

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

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

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Tree::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));

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::Tree::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>

Iterate over the tuples of keys and values in this tree.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Tree::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>

Iterate over tuples of keys and values, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Tree::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], vec![20]))));
// assert_eq!(iter.next(), Some(Ok((vec![3], vec![30]))));
// assert_eq!(iter.next(), None);

Important traits for Keys<'a>

Iterate over keys, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Tree::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);

Important traits for Values<'a>

Iterate over values, starting at the provided key.

Examples

let config = sled::ConfigBuilder::new().temporary(true).build();
let t = sled::Tree::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);

Returns the number of elements in this tree.

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

Returns true if the Tree contains no elements.

Trait Implementations

impl Clone for Tree
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Performs copy-assignment from source. Read more

impl Sync for Tree
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impl<'a> IntoIterator for &'a Tree
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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

impl Send for Tree
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impl Debug for Tree
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Blanket Implementations

impl<T> From for T
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impl<T, U> Into for T where
    U: From<T>, 
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impl<T> ToOwned for T where
    T: Clone
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impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> Borrow for T where
    T: ?Sized
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from)

The type returned in the event of a conversion error.

impl<T> BorrowMut for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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