slatedb 0.5.2

A cloud native embedded storage engine built on object storage.
Documentation 
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//! # Foyer Cache
//!
//! This module provides an implementation of an in-memory cache using the Foyer library.
//! The cache is designed to store and retrieve cached blocks, indexes, and bloom filters
//! associated with SSTable IDs.
//!
//! ## Features
//!
//! - **Asynchronous Operations**: Utilizes Foyer's `Cache` to perform cache operations asynchronously.
//! - **Custom Weigher**: Implements a custom weigher to account for the size of cached blocks.
//! - **Flexible Configuration**: Allows customization of cache parameters such as maximum capacity.
//!
//! ## Examples
//!
//! ```rust,no_run
//! use object_store::local::LocalFileSystem;
//! use slatedb::Db;
//! use slatedb::db_cache::foyer::{FoyerCache, FoyerCacheOptions};
//! use slatedb::config::DbOptions;
//! use std::sync::Arc;
//!
//! #[::tokio::main]
//! async fn main() {
//!     let object_store = Arc::new(LocalFileSystem::new());
//!     let options = DbOptions {
//!         block_cache: Some(Arc::new(FoyerCache::new())),
//!         ..Default::default()
//!     };
//!     let db = Db::open_with_opts("path/to/db", options, object_store).await;
//! }
//! ```
//!

use crate::db_cache::{CachedEntry, CachedKey, DbCache, DEFAULT_MAX_CAPACITY};
use async_trait::async_trait;

/// The options for the Foyer cache.
#[derive(Clone, Copy, Debug)]
pub struct FoyerCacheOptions {
    pub max_capacity: u64,
}

impl Default for FoyerCacheOptions {
    fn default() -> Self {
        Self {
            max_capacity: DEFAULT_MAX_CAPACITY,
        }
    }
}

/// A cache implementation using the Foyer library.
///
/// This struct wraps a Foyer cache, providing an in-memory caching solution
/// for storing and retrieving cached blocks associated with SSTable IDs.
///
/// # Fields
///
/// * `inner` - The underlying Foyer cache instance, which maps `CachedKey`
///   keys to `CachedEntry` values.
///
/// # Notes
///
/// The cache is configured based on the provided `FoyerCacheOptions`,
/// including settings for the maximum capacity of the cache.
/// It uses a custom weigher to account for the size of cached blocks.
pub struct FoyerCache {
    inner: foyer::Cache<CachedKey, CachedEntry>,
}

impl FoyerCache {
    pub fn new() -> Self {
        Self::new_with_opts(FoyerCacheOptions::default())
    }

    pub fn new_with_opts(options: FoyerCacheOptions) -> Self {
        let builder = foyer::CacheBuilder::new(options.max_capacity as _)
            .with_weighter(|_, v: &CachedEntry| v.size());

        let cache = builder.build();

        Self { inner: cache }
    }
}

impl Default for FoyerCache {
    fn default() -> Self {
        Self::new()
    }
}

#[async_trait]
impl DbCache for FoyerCache {
    async fn get_block(&self, key: CachedKey) -> Option<CachedEntry> {
        self.inner.get(&key).map(|entry| entry.value().clone())
    }

    async fn get_index(&self, key: CachedKey) -> Option<CachedEntry> {
        self.inner.get(&key).map(|entry| entry.value().clone())
    }

    async fn get_filter(&self, key: CachedKey) -> Option<CachedEntry> {
        self.inner.get(&key).map(|entry| entry.value().clone())
    }

    async fn insert(&self, key: CachedKey, value: CachedEntry) {
        self.inner.insert(key, value);
    }

    async fn remove(&self, key: CachedKey) {
        self.inner.remove(&key);
    }

    fn entry_count(&self) -> u64 {
        // foyer cache doesn't support an entry count estimate
        0
    }
}