lsm_tree/

lib.rs

// Copyright (c) 2024-present, fjall-rs
// This source code is licensed under both the Apache 2.0 and MIT License
// (found in the LICENSE-* files in the repository)

//! A K.I.S.S. implementation of log-structured merge trees (LSM-trees/LSMTs).
//!
//! ##### NOTE
//!
//! > This crate only provides a primitive LSM-tree, not a full storage engine.
//! > You probably want to use <https://crates.io/crates/fjall> instead.
//! > For example, it does not ship with a write-ahead log, so writes are not
//! > persisted until manually flushing the memtable.
//!
//! ##### About
//!
//! This crate exports a `Tree` that supports a subset of the `BTreeMap` API.
//!
//! LSM-trees are an alternative to B-trees to persist a sorted list of items (e.g. a database table)
//! on disk and perform fast lookup queries.
//! Instead of updating a disk-based data structure in-place,
//! deltas (inserts and deletes) are added into an in-memory write buffer (`Memtable`).
//! Data is then flushed to disk segments when the write buffer reaches some threshold.
//!
//! Amassing many segments on disk will degrade read performance and waste disk space, so segments
//! can be periodically merged into larger segments in a process called `Compaction`.
//! Different compaction strategies have different advantages and drawbacks, and should be chosen based
//! on the workload characteristics.
//!
//! Because maintaining an efficient structure is deferred to the compaction process, writing to an LSMT
//! is very fast (_O(1)_ complexity).
//!
//! Keys are limited to 65536 bytes, values are limited to 2^32 bytes. As is normal with any kind of storage
//! engine, larger keys and values have a bigger performance impact.
//!
//! # Example usage
//!
//! ```
//! use lsm_tree::{AbstractTree, Config, Tree};
//! #
//! # let folder = tempfile::tempdir()?;
//!
//! // A tree is a single physical keyspace/index/...
//! // and supports a BTreeMap-like API
//! let tree = Config::new(folder).open()?;
//!
//! // Note compared to the BTreeMap API, operations return a Result<T>
//! // So you can handle I/O errors if they occur
//! tree.insert("my_key", "my_value", /* sequence number */ 0);
//!
//! let item = tree.get("my_key", 1)?;
//! assert_eq!(Some("my_value".as_bytes().into()), item);
//!
//! // Search by prefix
//! for item in tree.prefix("prefix", 1, None) {
//!   // ...
//! }
//!
//! // Search by range
//! for item in tree.range("a"..="z", 1, None) {
//!   // ...
//! }
//!
//! // Iterators implement DoubleEndedIterator, so you can search backwards, too!
//! for item in tree.prefix("user1", 1, None).rev() {
//!   // ...
//! }
//!
//! // Flush to secondary storage, clearing the memtable
//! // and persisting all in-memory data.
//! // Note, this flushes synchronously, which may not be desired
//! tree.flush_active_memtable(0)?;
//!
//! // When some disk segments have amassed, use compaction
//! // to reduce the number of disk segments
//!
//! // Choose compaction strategy based on workload
//! use lsm_tree::compaction::Leveled;
//! # use std::sync::Arc;
//!
//! let strategy = Leveled::default();
//!
//! let version_gc_threshold = 0;
//! tree.compact(Arc::new(strategy), version_gc_threshold)?;
//! #
//! # Ok::<(), lsm_tree::Error>(())
//! ```

#![doc(html_logo_url = "https://raw.githubusercontent.com/fjall-rs/lsm-tree/main/logo.png")]
#![doc(html_favicon_url = "https://raw.githubusercontent.com/fjall-rs/lsm-tree/main/logo.png")]
#![deny(clippy::all, missing_docs, clippy::cargo)]
#![deny(clippy::unwrap_used)]
#![deny(clippy::indexing_slicing)]
#![warn(clippy::pedantic, clippy::nursery)]
#![warn(clippy::expect_used)]
#![allow(clippy::missing_const_for_fn)]
#![warn(clippy::multiple_crate_versions)]
#![allow(clippy::option_if_let_else)]
#![warn(clippy::redundant_feature_names)]
// the bytes feature uses unsafe to improve from_reader performance; so we need to relax this lint
// #![cfg_attr(feature = "bytes", deny(unsafe_code))]
// #![cfg_attr(not(feature = "bytes"), forbid(unsafe_code))]

pub(crate) type HashMap<K, V> = std::collections::HashMap<K, V, rustc_hash::FxBuildHasher>;
pub(crate) type HashSet<K> = std::collections::HashSet<K, rustc_hash::FxBuildHasher>;

#[allow(unused)]
macro_rules! set {
    ($($x:expr),+ $(,)?) => {
        [$($x),+].into_iter().collect::<HashSet<_>>()
    }
}

macro_rules! fail_iter {
    ($e:expr) => {
        match $e {
            Ok(v) => v,
            Err(e) => return Some(Err(e.into())),
        }
    };
}

mod any_tree;

mod r#abstract;

#[doc(hidden)]
pub mod binary_search;

#[doc(hidden)]
pub mod blob_tree;

#[doc(hidden)]
mod cache;

#[doc(hidden)]
pub mod coding;

pub mod compaction;
mod compression;

/// Configuration
pub mod config;

mod double_ended_peekable;

mod error;

pub(crate) mod fallible_clipping_iter;

#[doc(hidden)]
pub mod file;

mod hash;

mod iter_guard;

mod key;
mod key_range;

#[doc(hidden)]
pub mod level_manifest;

mod run_reader;
mod run_scanner;

mod manifest;
mod memtable;

#[doc(hidden)]
mod descriptor_table;

#[doc(hidden)]
pub mod merge;

#[cfg(feature = "metrics")]
pub(crate) mod metrics;

mod multi_reader;

#[doc(hidden)]
pub mod mvcc_stream;

mod path;

#[doc(hidden)]
pub mod range;

mod seqno;
mod slice;
mod slice_windows;

#[doc(hidden)]
pub mod stop_signal;

mod format_version;
mod time;
mod tree;
mod value;
mod version;
mod vlog;

#[doc(hidden)]
pub mod segment;

/// KV-tuple, typically returned by an iterator
pub type KvPair = (UserKey, UserValue);

#[doc(hidden)]
pub use key_range::KeyRange;

#[doc(hidden)]
pub use {
    merge::BoxedIterator,
    segment::{block::Checksum, GlobalSegmentId, Segment, SegmentId},
    tree::ingest::Ingestion,
    tree::inner::TreeId,
    value::InternalValue,
};

pub use {
    cache::Cache,
    coding::{DecodeError, EncodeError},
    compression::CompressionType,
    config::{Config, TreeType},
    descriptor_table::DescriptorTable,
    error::{Error, Result},
    format_version::FormatVersion,
    iter_guard::IterGuard as Guard,
    memtable::Memtable,
    r#abstract::AbstractTree,
    seqno::SequenceNumberCounter,
    tree::Tree,
    value::{SeqNo, ValueType},
    vlog::BlobFile,
};

#[cfg(feature = "metrics")]
pub use metrics::Metrics;

pub use any_tree::AnyTree;

pub use blob_tree::BlobTree;

pub use slice::Slice;

/// User defined key
pub type UserKey = Slice;

/// User defined data (byte array)
pub type UserValue = Slice;

/// Blob garbage collection utilities
pub mod gc {
    pub use super::vlog::{
        GcReport as Report, GcStrategy as Strategy, SpaceAmpStrategy, StaleThresholdStrategy,
    };
}

// TODO: investigate perf
macro_rules! unwrap {
    ($x:expr) => {{
        #[cfg(not(feature = "use_unsafe"))]
        {
            $x.expect("should read")
        }

        #[cfg(feature = "use_unsafe")]
        {
            unsafe { $x.unwrap_unchecked() }
        }
    }};
}

pub(crate) use unwrap;