Actix Rust deadpool_postgres: DB connections not released - postgresql

Question

I've got an Actix-web server that connects to a Postgres DB.
I've noticed that after a 1000 requests my Postgres DB's RAM usage has spiked.
When I stop actix-web, the RAM held by the db is cleared. This leads me to believe that my code is not releasing the connection.
I cannot find an example of connections actually being released. It looks like it's inferred in everyone else's code.
Here's mine:
async fn hellow_world(a : f32, b : f32, pool: &Pool) -> Result<Value, PoolError> {
let client: Client = pool.get().await?;
let sql = format!("select \"json\" from public.table_a WHERE a={} and b={}", a, b);
let stmt = client.prepare(&sql).await?;
let row = client.query_one(&stmt, &[]).await?;
let result : Value = row.get(0);
Ok(result)
}
#[derive(Deserialize)]
pub struct MyRequest {
a: f32,
b: f32
}
#[get("/hello")]
async fn sv_hellow_world(info: web::Query<MyRequest>, db_pool: web::Data<Pool>) -> Result<HttpResponse, Error> {
let response : Value = hellow_world(info.a, info.b, &db_pool).await?;
Ok(HttpResponse::Ok().json(response))
}
#[actix_rt::main]
async fn main() -> std::io::Result<()> {
dotenv().ok();
let config = Config::from_env().unwrap();
let pool = config.pg.create_pool(tokio_postgres::NoTls).unwrap();
env_logger::from_env(Env::default().default_filter_or("info")).init();
let server = HttpServer::new(move || App::new().wrap(Logger::default()).wrap(Logger::new("%a %{User-Agent}i")).data(pool.clone()).service(sv_hellow_world))
.bind("0.0.0.0:3000")?
.run();
server.await
}

Answer 1

Based on further testing, #Werner determined that the code was piling up server-side prepared statements.
It is not clear whether these statements can be closed using this library.
Either of two approaches can be used to avoid this problem:
Use a single, shared prepared statement
Use the direct query form instead of the prepared statement
I recommend the first approach on principle as it is more efficient and protects against SQL Injection. It should look something like this:
async fn hellow_world(a : f32, b : f32, pool: &Pool) -> Result<Value, PoolError> {
let client: Client = pool.get().await?;
let stmt = client.prepare("select \"json\" from public.table_a WHERE a=$1::numeric and b=$2::numeric").await?;
let row = client.query_one(&stmt, &[&a, &b]).await?;
let result : Value = row.get(0);
Ok(result)
}
Using this code, only one prepared statement should be created on each of the pool's connections.