# pagecache
[](https://travis-ci.org/spacejam/sled)
[](https://crates.io/crates/pagecache)
[](https://docs.rs/pagecache)
A construction kit for databases. Provides a lock-free log store and pagecache.
# References
* [LLAMA: A Cache/Storage Subsystem for Modern Hardware](https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/llama-vldb2013.pdf)
* [The Design and Implementation of a Log-Structured File System](https://people.eecs.berkeley.edu/~brewer/cs262/LFS.pdf)
```rust
use {
pagecache::{pin, Materializer, Config},
serde::{Serialize, Deserialize},
};
#[derive(
Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Serialize, Deserialize,
)]
pub struct TestState(String);
impl Materializer for TestState {
// Used to merge chains of partial pages into a form
// that is useful for the `PageCache` owner.
fn merge(&mut self, other: &TestState) {
self.0.push_str(&other.0);
}
}
fn main() {
let config = pagecache::ConfigBuilder::new().temporary(true).build();
let pc: pagecache::PageCache<TestState> =
pagecache::PageCache::start(config).unwrap();
{
// We begin by initiating a new transaction, which
// will prevent any witnessable memory from being
// reclaimed before we drop this object.
let tx = pc.begin().unwrap();
// The first item in a page should be set using allocate,
// which signals that this is the beginning of a new
// page history.
let (id, mut key) = pc.allocate(TestState("a".to_owned()), &tx).unwrap();
// Subsequent atomic updates should be added with link.
key = pc.link(id, key, TestState("b".to_owned()), &tx).unwrap().unwrap();
key = pc.link(id, key, TestState("c".to_owned()), &tx).unwrap().unwrap();
// When getting a page, the provided `Materializer` is
// used to merge all pages together.
let (mut key, page, size_on_disk) = pc.get(id, &tx).unwrap().unwrap();
assert_eq!(page.0, "abc".to_owned());
// You can completely rewrite a page by using `replace`:
key = pc.replace(id, key, TestState("d".into()), &tx).unwrap().unwrap();
let (key, page, size_on_disk) = pc.get(id, &tx).unwrap().unwrap();
assert_eq!(page.0, "d".to_owned());
}
}
```