Struct memory_db::MemoryDB

source · [−]
pub struct MemoryDB<H, KF, T, M = DefaultMemTracker<T>> where
    H: KeyHasher,
    KF: KeyFunction<H>,
    M: MemTracker<T>,  { /* private fields */ }
Expand description

Reference-counted memory-based HashDB implementation.

Use new() to create a new database. Insert items with insert(), remove items with remove(), check for existence with contains() and lookup a hash to derive the data with get(). Clear with clear() and purge the portions of the data that have no references with purge().

If you’re not using the MallocSizeOf implementation to track memory usage, set the M type parameter to NoopTracker.

Example

  use hash_db::{Hasher, HashDB, EMPTY_PREFIX};
  use keccak_hasher::KeccakHasher;
  use memory_db::{MemoryDB, HashKey};

  let mut m = MemoryDB::<KeccakHasher, HashKey<_>, Vec<u8>>::default();
  let d = "Hello world!".as_bytes();

  let k = m.insert(EMPTY_PREFIX, d);
  assert!(m.contains(&k, EMPTY_PREFIX));
  assert_eq!(m.get(&k, EMPTY_PREFIX).unwrap(), d);

  m.insert(EMPTY_PREFIX, d);
  assert!(m.contains(&k, EMPTY_PREFIX));

  m.remove(&k, EMPTY_PREFIX);
  assert!(m.contains(&k, EMPTY_PREFIX));

  m.remove(&k, EMPTY_PREFIX);
  assert!(!m.contains(&k, EMPTY_PREFIX));

  m.remove(&k, EMPTY_PREFIX);
  assert!(!m.contains(&k, EMPTY_PREFIX));

  m.insert(EMPTY_PREFIX, d);
  assert!(!m.contains(&k, EMPTY_PREFIX));
  m.insert(EMPTY_PREFIX, d);
  assert!(m.contains(&k, EMPTY_PREFIX));
  assert_eq!(m.get(&k, EMPTY_PREFIX).unwrap(), d);

  m.remove(&k, EMPTY_PREFIX);
  assert!(!m.contains(&k, EMPTY_PREFIX));

Implementations

Create a new MemoryDB from a given null key/data

Remove an element and delete it from storage if reference count reaches zero. If the value was purged, return the old value.

Shrinks the capacity of the map as much as possible. It will drop down as much as possible while maintaining the internal rules and possibly leaving some space in accordance with the resize policy.

Create a new MemoryDB from a given null key/data

Create a new instance of Self.

Create a new default instance of Self and returns Self and the root hash.

Clear all data from the database.

Examples
extern crate hash_db;
extern crate keccak_hasher;
extern crate memory_db;

use hash_db::{Hasher, HashDB, EMPTY_PREFIX};
use keccak_hasher::KeccakHasher;
use memory_db::{MemoryDB, HashKey};

fn main() {
  let mut m = MemoryDB::<KeccakHasher, HashKey<_>, Vec<u8>>::default();
  let hello_bytes = "Hello world!".as_bytes();
  let hash = m.insert(EMPTY_PREFIX, hello_bytes);
  assert!(m.contains(&hash, EMPTY_PREFIX));
  m.clear();
  assert!(!m.contains(&hash, EMPTY_PREFIX));
}

Purge all zero-referenced data from the database.

Return the internal key-value HashMap, clearing the current state.

Grab the raw information associated with a key. Returns None if the key doesn’t exist.

Even when Some is returned, the data is only guaranteed to be useful when the refs > 0.

Consolidate all the entries of other into self.

Get the keys in the database together with number of underlying references.

Trait Implementations

Perform upcast to HashDB for anything that derives from HashDB.

Perform mutable upcast to HashDB for anything that derives from HashDB.

Perform upcast to PlainDB for anything that derives from PlainDB.

Perform mutable upcast to PlainDB for anything that derives from PlainDB.

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Returns the “default value” for a type. Read more

Look up a given hash into the bytes that hash to it, returning None if the hash is not known. Read more

Check for the existance of a hash-key.

Like insert(), except you provide the key and the data is all moved.

Insert a datum item into the DB and return the datum’s hash for a later lookup. Insertions are counted and the equivalent number of remove()s must be performed before the data is considered dead. Read more

Remove a datum previously inserted. Insertions can be “owed” such that the same number of insert()s may happen without the data being eventually being inserted into the DB. It can be “owed” more than once. Read more

Look up a given hash into the bytes that hash to it, returning None if the hash is not known. Read more

Check for the existance of a hash-key.

Measure the heap usage of all descendant heap-allocated structures, but not the space taken up by the value itself. If T::size_of is a constant, consider implementing constant_size as well. Read more

Used to optimize MallocSizeOf implementation for collections like Vec and HashMap to avoid iterating over them unnecessarily. The Self: Sized bound is for object safety. Read more

This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

Look up a given hash into the bytes that hash to it, returning None if the hash is not known. Read more

Check for the existance of a hash-key.

Insert a datum item into the DB. Insertions are counted and the equivalent number of remove()s must be performed before the data is considered dead. The caller should ensure that a key only corresponds to one value. Read more

Remove a datum previously inserted. Insertions can be “owed” such that the same number of insert()s may happen without the data being eventually being inserted into the DB. It can be “owed” more than once. The caller should ensure that a key only corresponds to one value. Read more

Look up a given hash into the bytes that hash to it, returning None if the hash is not known. Read more

Check for the existance of a hash-key.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more

Immutably borrows from an owned value. Read more

Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

Method to launch a heapsize measurement with a fresh state. Read more

The resulting type after obtaining ownership.

Creates owned data from borrowed data, usually by cloning. Read more

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

Uses borrowed data to replace owned data, usually by cloning. Read more

The type returned in the event of a conversion error.

Performs the conversion.

The type returned in the event of a conversion error.

Performs the conversion.