Struct KvStore 

pub struct KvStore<S: Storage> { /* private fields */ }

A versioned key-value store using a log-structured hash table.

Reads and writes serde keys and values. All reads/writes happen through transactions. A store can be merged to discard old versions and thus store a more compact representation containing only the latest version of each key-value pair.

Versions are also used to implement a “move to trash” behavior. Whenever a value is removed, it is not purged from storage but simply marked as removed. It remains accessible until the “trash is emptied” during the next merge. As a consequence there are 2 different methods that can read values from the store, depending on whether the trash should be included or not, Snapshot::get() (which will return None if the value was “moved to the trash”) and Snapshot::get_unremoved() (which will return the last unremoved version if the value was “moved to the trash”).

• Keys/values are Serialize/Deserialize and are serialized/deserialized to/from MessagePack using rmp-serde.
• Keys are not read/written as-is, but always associated with a “slot”. These slots act as the different “indexes” of a store.

Implementations

impl<S: Storage> KvStore<S>

pub async fn open(storage: S) -> Result<Self>

Opens and reads a store from storage.

If no store exists at the storage location, a new store will be initialized. Otherwise, the store will be read and checked for corrupted data. In case of corruption, everything after the corrupted offset will be truncated and later writes will overwrite the corrupted entries. After the initial read, a hash table of all the keys in the store and their storage offsets is kept in memory.

pub fn name(&self) -> &str

Returns the (file-)name of the storage.

pub fn into_storage(self) -> Result<S>

Consumes the store to return its underlying storage.

pub async fn len(&self) -> u64

Returns the total length of the storage in bytes.

pub async fn is_empty(&self) -> bool

Returns true if the storage is empty.

pub async fn current(&self) -> Snapshot<'_, S>

Creates a transactional read-write snapshot of the store at the current point in time, see Snapshot.

pub async fn merge(&mut self) -> Result<()>

Merges and compacts the store by removing old versions.

Merging a store reclaims space by removing all versions that were superseded by newer writes to the same key. As a side effect, a merge “empties the trash” and ensures that removed values cannot be read and restored anymore.