# r2d2
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A generic connection pool for Rust.

[Documentation](https://docs.rs/r2d2)

Opening a new database connection every time one is needed is both inefficient
and can lead to resource exhaustion under high traffic conditions. A connection
pool maintains a set of open connections to a database, handing them out for
repeated use.

r2d2 is agnostic to the connection type it is managing. Implementors of the
`ManageConnection` trait provide the database-specific logic to create and
check the health of connections.

A (possibly not exhaustive) list of adaptors for different backends:

Backend                                                                | Adaptor Crate
---------------------------------------------------------------------- | -------------
[rust-postgres](https://github.com/sfackler/rust-postgres)             | [r2d2-postgres](https://github.com/sfackler/r2d2-postgres)
[redis-rs](https://github.com/mitsuhiko/redis-rs)                      | use `r2d2` feature of [redis-rs](https://github.com/mitsuhiko/redis-rs)
[rust-memcache](https://github.com/aisk/rust-memcache)                 | [r2d2-memcache](https://github.com/megumish/r2d2-memcache)
[rust-mysql-simple](https://github.com/blackbeam/rust-mysql-simple)    | [r2d2-mysql](https://github.com/outersky/r2d2-mysql)
[rusqlite](https://github.com/jgallagher/rusqlite)                     | [r2d2-sqlite](https://github.com/ivanceras/r2d2-sqlite)
[rsfbclient](https://github.com/fernandobatels/rsfbclient)                     | [r2d2-firebird](https://crates.io/crates/r2d2_firebird/)
[rusted-cypher](https://github.com/livioribeiro/rusted-cypher)         | [r2d2-cypher](https://github.com/flosse/r2d2-cypher)
[diesel](https://github.com/sgrif/diesel)                              | [diesel::r2d2](https://github.com/diesel-rs/diesel/blob/master/diesel/src/r2d2.rs) ([docs](https://docs.diesel.rs/diesel/r2d2/))
[couchdb](https://github.com/chill-rs/chill)                           | [r2d2-couchdb](https://github.com/scorphus/r2d2-couchdb)
[mongodb (archived)](https://github.com/mongodb-labs/mongo-rust-driver-prototype)<br>use official [mongodb](https://github.com/mongodb/mongo-rust-driver) driver instead                             | [r2d2-mongodb](https://gitlab.com/petoknm/r2d2-mongodb)<br>(deprecated: official driver handles pooling internally)
[odbc](https://github.com/Koka/odbc-rs)                                | [r2d2-odbc](https://github.com/Koka/r2d2-odbc)
[jfs](https://github.com/flosse/rust-json-file-store)                  | [r2d2-jfs](https://github.com/flosse/r2d2-jfs)
[oracle](https://github.com/kubo/rust-oracle)                          | [r2d2-oracle](https://github.com/rursprung/r2d2-oracle)
[ldap3](https://github.com/inejge/ldap3)                               | [r2d2-ldap](https://github.com/c0dearm/r2d2-ldap)
[duckdb-rs](https://github.com/wangfenjin/duckdb-rs)                   | use `r2d2` feature of [duckdb-rs](https://github.com/wangfenjin/duckdb-rs)

# Example

Using an imaginary "foodb" database.

```rust
use std::thread;

extern crate r2d2;
extern crate r2d2_foodb;

fn main() {
    let manager = r2d2_foodb::FooConnectionManager::new("localhost:1234");
    let pool = r2d2::Pool::builder()
        .max_size(15)
        .build(manager)
        .unwrap();

    for _ in 0..20 {
        let pool = pool.clone();
        thread::spawn(move || {
            let conn = pool.get().unwrap();
            // use the connection
            // it will be returned to the pool when it falls out of scope.
        })
    }
}
```

## License

Licensed under either of
 * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
 * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)

at your option.

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you shall be dual licensed as above, without any
additional terms or conditions.