Struct MemoryStore 

pub struct MemoryStore { /* private fields */ }

An in-memory VersionStore that shards the keyspace for concurrency.

Each key is hashed to one of a fixed number of shards; each shard holds its keys’ version chains behind its own reader-writer lock. Reads lock a single shard; a commit locks only the shards its keys fall in. Commits to disjoint shards therefore run in parallel, and the snapshot read of a key is a binary search within its shard for the newest version at or below the snapshot timestamp.

This is the default store of Db::new and suits caches, tests, and workloads that fit in memory. Versions accumulate until garbage collection lands (a later roadmap phase), so a long-lived store under heavy overwrite grows without bound for now.

Examples

use txn_db::{Db, MemoryStore};

// `Db::new()` uses a `MemoryStore`; this is the explicit form.
let db = Db::with_store(MemoryStore::new());
let mut tx = db.begin();
tx.put(b"hello".to_vec(), b"world".to_vec());
tx.commit()?;

Implementations

impl MemoryStore

pub fn new() -> Self

Create an empty in-memory store with the default shard count.

Examples

use txn_db::MemoryStore;

let store = MemoryStore::new();

pub fn with_shards(shards: usize) -> Self

Create an empty store with a specific number of shards.

shards is rounded up to a power of two (and at least one). More shards reduce contention between commits that touch unrelated keys, at the cost of a larger fixed footprint. The default of MemoryStore::new suits most workloads; tune this only with a benchmark in hand.

Examples

use txn_db::MemoryStore;

let store = MemoryStore::with_shards(64);

pub fn key_count(&self) -> usize

Number of distinct keys that have ever been written.

Counts keys, not versions, and includes keys whose latest version is a tombstone. Primarily useful in tests and diagnostics.

Examples

use txn_db::MemoryStore;

let store = MemoryStore::new();
assert_eq!(store.key_count(), 0);

Trait Implementations

impl Default for MemoryStore

fn default() -> Self

Returns the “default value” for a type.

impl VersionStore for MemoryStore

fn get(&self, key: &[u8], read_ts: Timestamp) -> Result<Option<Arc<[u8]>>>

Return the value of key visible at read_ts.

fn try_commit( &self, read_ts: Timestamp, commit_ts: Timestamp, writes: Vec<WriteEntry>, reads: &[Arc<[u8]>], ) -> Result<()>

Validate a transaction and, if it does not conflict, apply its writes.