Crate mobc

A generic connection pool with async/await support.

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.

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

Example

Using an imaginary “foodb” database.

use mobc::{Manager, Pool, async_trait};

#[derive(Debug)]
struct FooError;

struct FooConnection;

impl FooConnection {
   async fn query(&self) -> String {
       "nori".to_string()
   }
}

struct FooManager;

#[async_trait]
impl Manager for FooManager {
   type Connection = FooConnection;
   type Error = FooError;

   async fn connect(&self) -> Result<Self::Connection, Self::Error> {
       Ok(FooConnection)
   }

   async fn check(&self, conn: Self::Connection) -> Result<Self::Connection, Self::Error> {
       Ok(conn)
   }
}

#[tokio::main]
async fn main() {
   let pool = Pool::builder().max_open(15).build(FooManager);
   let num: usize = 10000;
   let (tx, mut rx) = tokio::sync::mpsc::channel::<()>(16);

   for _ in 0..num {
       let pool = pool.clone();
       let mut tx = tx.clone();
       tokio::spawn(async move {
           let conn = pool.get().await.unwrap();
           let name = conn.query().await;
           assert_eq!(name, "nori".to_string());
           tx.send(()).await.unwrap();
       });
   }

   for _ in 0..num {
       rx.recv().await.unwrap();
   }
}

Metrics

Mobc uses the metrics crate to expose the following metrics

1. Active Connections - The number of connections in use.
2. Idle Connections - The number of connections that are not being used
3. Wait Count - the number of processes waiting for a connection
4. Wait Duration - A cumulative histogram of the wait time for a connection

Modules

runtime

A batteries included runtime for applications using mobc. Mobc does not implement runtime, it simply exports runtime.

Structs

Builder

A builder for a connection pool.

Connection

A smart pointer wrapping a connection.

Pool

A generic connection pool.

State

Information about the state of a Pool.

Enums

Error

The error type returned by methods in this crate.

Traits

Manager

A trait which provides connection-specific functionality.

Functions

spawn

Spawns a new asynchronous task.

Attribute Macros

async_trait