Crate bb8

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A full-featured connection pool, designed for asynchronous connections (using tokio). Originally based on 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.

bb8 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.


Using an imaginary “foodb” database.

async fn main() {
    let manager = bb8_foodb::FooConnectionManager::new("localhost:1234");
    let pool = bb8::Pool::builder().build(manager).await.unwrap();

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


  • A builder for a connection pool.
  • An ErrorSink implementation that does nothing.
  • A generic connection pool.
  • A smart pointer wrapping a connection.
  • Information about the state of a Pool.
  • Statistics about the historical usage of the Pool.



  • A trait which provides functionality to initialize a connection
  • A trait to receive errors generated by connection management that aren’t tied to any particular caller.
  • A trait which provides connection-specific functionality.