Expand description
A simple, humane, typed key-value storage solution. It supports multiple backend engines with varying guarantees, such as LMDB for performance, or “SafeMode” for reliability.
It aims to achieve the following:
- Avoid sharp edges (e.g., obscure error codes for common situations).
- Correctly restrict access to one handle per process via a Manager.
- Use Rust’s type system to make single-typed key stores safe and ergonomic.
- Encode and decode values via bincode/serde and type tags, achieving platform-independent storage and input/output flexibility.
It exposes these primary abstractions:
- Manager: a singleton that controls access to environments
- Rkv: an environment contains a set of key/value databases
- SingleStore: a database contains a set of key/value pairs
Keys can be anything that implements AsRef<[u8]>
or integers
(when accessing an IntegerStore).
Values can be any of the types defined by the Value enum, including:
- booleans (
Value::Bool
) - integers (
Value::I64
,Value::U64
) - floats (
Value::F64
) - strings (
Value::Str
) - blobs (
Value::Blob
)
See Value for the complete list of supported types.
Basic Usage
use rkv::{Manager, Rkv, SingleStore, Value, StoreOptions};
use rkv::backend::{SafeMode, SafeModeEnvironment};
use std::fs;
use tempfile::Builder;
// First determine the path to the environment, which is represented on disk as a
// directory containing two files:
//
// * a data file containing the key/value stores
// * a lock file containing metadata about current transactions
//
// In this example, we use the `tempfile` crate to create the directory.
//
let root = Builder::new().prefix("simple-db").tempdir().unwrap();
fs::create_dir_all(root.path()).unwrap();
let path = root.path();
// The `Manager` enforces that each process opens the same environment at most once by
// caching a handle to each environment that it opens. Use it to retrieve the handle
// to an opened environment—or create one if it hasn't already been opened:
let mut manager = Manager::<SafeModeEnvironment>::singleton().write().unwrap();
let created_arc = manager.get_or_create(path, Rkv::new::<SafeMode>).unwrap();
let env = created_arc.read().unwrap();
// Then you can use the environment handle to get a handle to a datastore:
let store = env.open_single("mydb", StoreOptions::create()).unwrap();
{
// Use a write transaction to mutate the store via a `Writer`. There can be only
// one writer for a given environment, so opening a second one will block until
// the first completes.
let mut writer = env.write().unwrap();
// Keys are `AsRef<[u8]>`, while values are `Value` enum instances. Use the `Blob`
// variant to store arbitrary collections of bytes. Putting data returns a
// `Result<(), StoreError>`, where StoreError is an enum identifying the reason
// for a failure.
store.put(&mut writer, "int", &Value::I64(1234)).unwrap();
store.put(&mut writer, "uint", &Value::U64(1234_u64)).unwrap();
store.put(&mut writer, "float", &Value::F64(1234.0.into())).unwrap();
store.put(&mut writer, "instant", &Value::Instant(1528318073700)).unwrap();
store.put(&mut writer, "boolean", &Value::Bool(true)).unwrap();
store.put(&mut writer, "string", &Value::Str("Héllo, wörld!")).unwrap();
store.put(&mut writer, "json", &Value::Json(r#"{"foo":"bar", "number": 1}"#)).unwrap();
store.put(&mut writer, "blob", &Value::Blob(b"blob")).unwrap();
// You must commit a write transaction before the writer goes out of scope, or the
// transaction will abort and the data won't persist.
writer.commit().unwrap();
}
{
// Use a read transaction to query the store via a `Reader`. There can be multiple
// concurrent readers for a store, and readers never block on a writer nor other
// readers.
let reader = env.read().expect("reader");
// Keys are `AsRef<u8>`, and the return value is `Result<Option<Value>, StoreError>`.
println!("Get int {:?}", store.get(&reader, "int").unwrap());
println!("Get uint {:?}", store.get(&reader, "uint").unwrap());
println!("Get float {:?}", store.get(&reader, "float").unwrap());
println!("Get instant {:?}", store.get(&reader, "instant").unwrap());
println!("Get boolean {:?}", store.get(&reader, "boolean").unwrap());
println!("Get string {:?}", store.get(&reader, "string").unwrap());
println!("Get json {:?}", store.get(&reader, "json").unwrap());
println!("Get blob {:?}", store.get(&reader, "blob").unwrap());
// Retrieving a non-existent value returns `Ok(None)`.
println!("Get non-existent value {:?}", store.get(&reader, "non-existent").unwrap());
// A read transaction will automatically close once the reader goes out of scope,
// so isn't necessary to close it explicitly, although you can do so by calling
// `Reader.abort()`.
}
{
// Aborting a write transaction rolls back the change(s).
let mut writer = env.write().unwrap();
store.put(&mut writer, "foo", &Value::Str("bar")).unwrap();
writer.abort();
let reader = env.read().expect("reader");
println!("It should be None! ({:?})", store.get(&reader, "foo").unwrap());
}
{
// Explicitly aborting a transaction is not required unless an early abort is
// desired, since both read and write transactions will implicitly be aborted once
// they go out of scope.
{
let mut writer = env.write().unwrap();
store.put(&mut writer, "foo", &Value::Str("bar")).unwrap();
}
let reader = env.read().expect("reader");
println!("It should be None! ({:?})", store.get(&reader, "foo").unwrap());
}
{
// Deleting a key/value pair also requires a write transaction.
let mut writer = env.write().unwrap();
store.put(&mut writer, "foo", &Value::Str("bar")).unwrap();
store.put(&mut writer, "bar", &Value::Str("baz")).unwrap();
store.delete(&mut writer, "foo").unwrap();
// A write transaction also supports reading, and the version of the store that it
// reads includes the changes it has made regardless of the commit state of that
// transaction.
// In the code above, "foo" and "bar" were put into the store, then "foo" was
// deleted so only "bar" will return a result when the database is queried via the
// writer.
println!("It should be None! ({:?})", store.get(&writer, "foo").unwrap());
println!("Get bar ({:?})", store.get(&writer, "bar").unwrap());
// But a reader won't see that change until the write transaction is committed.
{
let reader = env.read().expect("reader");
println!("Get foo {:?}", store.get(&reader, "foo").unwrap());
println!("Get bar {:?}", store.get(&reader, "bar").unwrap());
}
writer.commit().unwrap();
{
let reader = env.read().expect("reader");
println!("It should be None! ({:?})", store.get(&reader, "foo").unwrap());
println!("Get bar {:?}", store.get(&reader, "bar").unwrap());
}
// Committing a transaction consumes the writer, preventing you from reusing it by
// failing at compile time with an error. This line would report "error[E0382]:
// borrow of moved value: `writer`".
// store.put(&mut writer, "baz", &Value::Str("buz")).unwrap();
}
{
// Clearing all the entries in the store with a write transaction.
{
let mut writer = env.write().unwrap();
store.put(&mut writer, "foo", &Value::Str("bar")).unwrap();
store.put(&mut writer, "bar", &Value::Str("baz")).unwrap();
writer.commit().unwrap();
}
{
let mut writer = env.write().unwrap();
store.clear(&mut writer).unwrap();
writer.commit().unwrap();
}
{
let reader = env.read().expect("reader");
println!("It should be None! ({:?})", store.get(&reader, "foo").unwrap());
println!("It should be None! ({:?})", store.get(&reader, "bar").unwrap());
}
}
Re-exports
pub use backend::DatabaseFlags;
pub use backend::EnvironmentFlags;
pub use backend::WriteFlags;
pub use store::keys::EncodableKey;
pub use store::single::SingleStore;
pub use store::CloseOptions;
pub use store::Options as StoreOptions;
pub use value::OwnedValue;
pub use value::Value;
pub use store::multi::MultiStore;
pub use store::integer::IntegerStore;
pub use store::keys::PrimitiveInt;
pub use store::integermulti::MultiIntegerStore;
Modules
Structs
- A process is only permitted to have one open handle to each Rkv environment. This manager exists to enforce that constraint: don’t open environments directly.
- Wrapper around an
Environment
(e.g. such as anLMDB
orSafeMode
environment).